Add copyright & license information to installed files
stbt config: New command-line tool to read a value from stbt config file

If you write your own shell scripts around stb-tester, you can store
settings in the same stbt.conf file that has the stbt settings like
"source_pipeline" and "control", and use `stbt config` to access those
settings.

This will be used by the upcoming tools proposed in
https://groups.google.com/forum/?fromgroups=#!topic/stb-tester/AI8kEmIY-z8

Note that the stbt-completion (bash tab-completion) unit tests run from
`make check-bashcompletion` now have to be run with bash, because they
use bash-specific features like <(process substitution).
New function `stbt.get_config` for stbt scripts to read from stbt.conf

At YouView we have been writing libraries of helper functions, like
"network.disable()" to control the network connectivity of our
system-under-test. So far we have been using environment variables to
let those libraries know, for example, the network interface of the
system-under-test, so that we can run the same stbt script and the same
library, without modification, against multiple different set-top boxes.

So we've ended up with some information in stbt.conf (e.g.
source-pipeline, which is different for each system-under-test because
the "/dev/videoN" device is different) and some information in
environment variables.

Thanks to this new `stbt.get_config` function we can store all the
information in stbt.conf, and have our custom libraries read from it.
Then if we have multiple set-top-boxes connected to a single PC, we
create a different stbt.conf for each one, and set STBT_CONFIG_FILE
appropriately in the environment of `stbt run`.

Note that `stbt.load_config` only reads the config files once, at the
beginning of `stbt run`, to ensure that the stbt script sees a
consistent view of the configuration files for the duration of its run.

Note that (unlike `stbt.wait_for_match` etc) stbt-run doesn't import
`get_config` into the top-level namespace of the stbt script, because
we want to encourage people to import dependencies into their scripts
explicitly (see commit 35bbf455).
stbt tv: New command-line tool to show live video on screen

`stbt tv` is useful when you have multiple systems-under-test and you
don't have a video multiplexer or switcher to connect them all to their
own TV monitor. With `stbt tv` you can view the system-under-test's
video output on your computer. This can't be used at the same time as
`stbt run`.
stbt screenshot: New command-line tool to capture a single screenshot

When you already have a large library of tests & helper functions,
writing a new test may only require one or two new template images, and
`stbt record` is overkill. This tool captures a screenshot from the
system-under-test in its current state.

This tool is also extremely useful immediately after a stbt script has
failed due to a false-failure from stb-tester's image-matching
algorithm: Unlike the screenshot generated by `stbt run` when a
`wait_for_match` fails, this screenshot won't have the "best match"
yellow rectangle drawn on it.
stbt templatematch: New command-line tool to compare two images

This is useful for experimenting with different `wait_for_match`
parameters, and for writing unit tests for your stbt scripts.

(Whenever we write a stbt script that has to override the wait_for_match
`noise_threshold`, we capture a screenshot and write a unit test —using
`stbt templatematch`— that will fail if the image comparison starts
matching _without_ the custom `noise_threshold`. That way we'll know to
remove the custom `noise_threshold` if the templatematch algorithm is
improved in a future release of stbt. The unit test also serves as
documentation for why the custom `noise_threshold` was necessary.)
Merge branch 'auxiliary-tools'

Implements some of the tools proposed in
https://groups.google.com/d/msg/stb-tester/AI8kEmIY-z8/xgCaonXNeDAJ

* auxiliary-tools:
  stbt templatematch: New command-line tool to compare two images
  stbt screenshot: New command-line tool to capture a single screenshot
  stbt tv: New command-line tool to show live video on screen
  New function `stbt.get_config` for stbt scripts to read from stbt.conf
  stbt config: New command-line tool to read a value from stbt config file