stbt.wait_for_motion: Change default `consecutive_frames` from 10 to '10/20'

As promised in the 0.12 release notes:
http://stb-tester.com/release-notes.html#0.12

See 84a795e8 for why this is more robust.
test_wait_for_match_confirm_method_none...: Remove unused import

Unused since commit eec38be8.
stbt control: New tool to send remote control commands with PC keyboard

This tool is useful when multiple set-top-boxes are under test in the
same room, and it is not safe to use the remote control shipped with
the box to control one because the IR signals are received by multiple
set-top-boxes.

The tool uses the same remote control implementations as 'stbt run'.

A keymap file is required to save mappings of keyboard keys to remote
control keys. It was designed to make it easy to create one from scratch
manually. See `stbt control --help` for detailed information.

It also has a non-interactive mode to send a remote control key from the
command line.

Note that we chose "//" for comments in the keymap file (instead of the
more common "#") to allow using the "#" keyboard key.
README: Clarify the `--control=lirc:` parameter
stbt.py: Cleanup: Sort imports alphabetically
stbt.detect_motion: Change wording of debug message

For consistency with stbt.detect_match.
"detect_match" and "detect_motion" implemented using the OpenCV Python bindings

...instead of listening for messages from the GStreamer elements
stbt-templatematch and stbt-motiondetect.

ADVANTAGES:

* Much simpler implementation (see the commit where we remove the
  GStreamer elements, later in this commit series). In particular the
  communication between the GStreamer element and the python code has
  caused us difficulties; see for example the implementation of
  "process_all_frames" in https://github.com/drothlis/stb-tester/pull/8

* Much more flexible: We'll be able to expose the sequence of frames as
  OpenCV images directly to the user script, for arbitrary image
  processing (for example you might want to detect black screens to
  measure channel change times; this is a trivial image processing
  operation of mask + threshold + count non-zero pixels).

REGRESSIONS IN FUNCTIONALITY:

* The GObject main loop isn't run, so we don't receive GStreamer
  over-/under-run signals, nor GObject timeouts.
* No red/yellow rectangle drawn on the output video.
* stbt-debug debug images aren't saved.

These will be addressed in subsequent commits in this series.

PERFORMANCE:

The script "tests/run-performance-test.sh" prints the frames-per-second
processed by "detect_match" against a video provided by the user (not
committed to the repository). Using a 720p video captured via the
Hauppauge HD PVR, on my dual-core Intel Core i7 MacBook Air this script
reports on average 3.6 frames per second with the python version, versus
3.8 frames per second with the original version (from 20 runs each).
stbt.py: Log intermediate images to disk

This brings back the "stbt run -vv" behaviour that was lost in commit
0f0dc1a6.
stbt._log_image: Scale "matchTemplate" image to visible range

The result of "cv2.matchTemplate" is a matrix with each pixel in the
range [0.0, 1.0]. This change scales the debug image saved to disk
to the grayscale range [0, 255].

Note that "_log_image" reassigns the name "image" to the scaled version,
but this name is local to the function. The scaling isn't done in-place,
so the original image isn't modified (otherwise the
"first_pass_certainty" comparison in "_match_template" would fail).
stbt.get_frame and stbt.save_frame return/operate on OpenCV format

"stbt.get_frame" returns an OpenCV image (i.e. a numpy array) instead of
a GStreamer buffer. The OpenCV image doesn't have any timestamp
information, unlike the GStreamer buffer; but I don't think anyone was
using that timestamp (if you wanted the timestamp you would have been
using "detect_match" or "detect_motion" instead).

"stbt.save_frame" takes an OpenCV image instead of a GStreamer buffer, and
uses the much simpler "cv2.imwrite" to save it to disk.

Note that "stbt.get_frame()" can no longer be used in a boolean context;
stbt-run's "if e.screenshot" would now fail with:

    ValueError: The truth value of an array with more than one element
    is ambiguous. Use a.any() or a.all()
test_get_frame_and_save_frame: Clearer error message

Instead of an obscure error message from the following "stbt-run"
command.

Note that "fail", which is to be used from test cases, can safely use
"exit" because each test case is run inside a sub-shell.
stbt.py: Run GLib main loop continuously, and wait on appsink "new-buffer" signals

...instead of polling appsink's "last-buffer" property.

Now we will monitor pipeline signals & messages like "underrun" all the
time, not just when inside a call to "wait_for_match" (or "detect_match",
"wait_for_motion", etc). So, for example, we will restart the pipeline
when we lose video input (see b6135eca) as soon as we detect video loss,
not just at the next "wait_for_match".

The GLib main loop is now running in a separate thread (not in the main
application thread, which runs the user's script), so "sys.exit" doesn't
work (it only raises a SystemExit exception, which terminates the thread
but isn't propagated to the main application thread). So we use the same
synchronised Queue that we use to communicate new frames to the main
application thread, for also communicating errors (in the form of
Exception objects).
stbt.py: Restart video pipeline as many times as it takes

We restart the source pipeline whenever video signal is lost to work
around the HD PVR behaviour where the device stops delivering video
when it loses input signal momentarily; see b6135eca.

With this commit, instead of giving up after 3 restart attempts, we rely
on the timeout in "Display.frames".

Before commit 78f3b221, video loss *outside* of a "wait_for_match" (or
"detect_match", "wait_for_motion", etc) didn't trigger the
pipeline-restart mechanism nor the exit-after-3-restarts. It was only
when you called "wait_for_match" (etc) that the 3 restarts were
attempted. We have test scripts that restart the system-under-test, and
it takes longer than the 3 restart attempts before the rebooted system
starts delivering video again, so our test scripts looked like this:

    restart_the_system_under_test()
    time.sleep(30)
    stbt.wait_for_match(...)

Since commit 78f3b221, we restart the video pipeline as soon as we
detect that we have lost video. This is desirable behaviour, because it
means that the next "wait_for_match" after a "sleep" (or other
processing) can start consuming video immediately, but the above script
would now exit during the "time.sleep" call. With this current commit,
the script will only exit due to "no video available" when it is inside
"wait_for_match" etc.  Note that you can set your own timeout to
"wait_for_match":

    restart_the_system_under_test()
    stbt.wait_for_match(..., timeout_secs=30)
stbt.py: Cleanup: Rename appsink element from "screenshot" to "appsink"

"Screenshot" is the purpose of the element, but it is potentially
confusing because "screenshot" usually means a single frame once
captured. If you know GStreamer then you know what "appsink" is.
stbt.Display.__init__: Remove unneeded member variables

"self.bus", "self.queue" and "self.mainloop_thread" aren't used outside
of this function.
stbt.detect_motion: Fix invalid argument on some versions of numpy

On travis-ci's Ubuntu 12.04 (?) the test
"test_wait_for_motion_with_mask_reports_motion" was complaining:
"TypeError: <unknown> is not a numpy array".
stbt-record: Update to use new stbt.py

"stbt record" stopped working since ef12d130.

This commit fixes that, and also takes advantage of the same
recover-from-video-loss capability that "stbt run" has (see commit
801d912f). It's also a lot less code!
Remove GStreamer plugin files

All image processing is now done in stbt.py, using the OpenCV python
bindings (see commit 0f0dc1a6).
Cleanup: Split tests/test-stbt-run.sh into test-{match,motion,stbt-py}.sh

"test-stbt-run.sh" was getting quite long (650 lines) and the
motion-related tests weren't all grouped together, so it seemed a good
idea to clean this up.
Remove tests for GStreamer temlatematch and motiondetect elements

The GStreamer elements were removed in commit a35848f2.

Added tests to "test-motion.sh" for functionality that was only covered
in the GStreamer element tests.