README: Note opencv-python dependency; don't mention GStreamer elements

All image processing is now done in python code in stbt.py (0f0dc1a6),
and we no longer use any custom GStreamer elements (a35848f2).

Our image processing algorithm was always a custom one we developed
ourselves; the original GStreamer templatematch element merely called
the OpenCV "matchTemplate" function. So we no longer have any code
originating from the gstreamer-opencv project.
Travis CI: Don't install gstreamer0.10-ffmpeg or -plugins-bad

stb-tester and its unit tests don't require this; it's only necessary if
the user's "source pipeline" uses ffmpeg GStreamer elements.

We do need gstreamer0.10-plugins-base for videotestsrc etc (presumably
this was an implicit dependency of -plugins-base or -ffmpeg).
Travis CI: Remove GStreamer dev packages

We no longer build GStreamer plugins (since a35848f).
Disable Travis CI (remove .travis.yml config file)

travis-ci.org is a free continuous-integration service. I've disabled
it because "test_wait_for_motion_with_mask_does_not_report_motion"
fails, possibly due to a bug in OpenCV 2.3:
http://answers.opencv.org/question/15279/

And we run "make check" ourselves during development anyway. We do lose
the opportunity to test on Ubuntu; but if "make check" always fails on
travis-ci, it has no value.

Travis-ci uses Ubuntu 12.04 LTS, which has OpenCV 2.3. I tried to
install OpenCV 2.4 from this PPA:
https://launchpad.net/~limparissoft/+archive/opencv-ppa

by applying the following patch to .travis.yml:

    diff --git a/.travis.yml b/.travis.yml
    index b00a049..3c481e6 100644
    --- a/.travis.yml
    +++ b/.travis.yml
    @@ -1,6 +1,7 @@
     language: c

     install:
    + - sudo add-apt-repository ppa:limparissoft/opencv-ppa
      - sudo apt-get update
      - sudo apt-get install gstreamer0.10-plugins-bad gstreamer0.10-ffmpeg
                             libgstreamer0.10-dev python-gst0.10 python-docutils
    @@ -8,7 +9,7 @@ install:
                             libcv-dev libhighgui-dev python-nose xvfb
                             gstreamer0.10-tools gstreamer0.10-x
                             gstreamer0.10-plugins-good pylint pep8
    -                        python-numpy python-opencv
    +                        opencv=2.4.5-0~3~precise1 python-numpy python-opencv
      - make

     script:

but it fails to install due to a conflict with opencv 2.3 (installed as
a dependency of python-opencv; the PPA doesn't have a 2.4 package for
python-opencv).
rpm spec file: Require opencv >= 2.4

Because of an intermittent bug that I can only reproduce on 2.3:
http://answers.opencv.org/question/15279

The bug manifests since we began using the OpenCV python bindings
(0f0dc1a6).
rpm spec file: GStreamer plugin no longer built

I forgot to remove this from a35848f2.