Added option to launch mplayer in the background to play videos.

The Raspberry Pi browsers cannot yet play video. But mplayer works on the
Pi, so we can trigger it to be launched when the user wants to view a
video. Point tracking is done in the backend Python thread that launched
mplayer, and the browser refreshes the point total when mplayer is closed.

Add `USE_MPLAYER = True` to local_settings.py to enabled this. Note that
it will only work when the browser is on the same computer as the server.
Merge branch 'develop' of github.com:learningequality/ka-lite into mplayer_launcher

Conflicts:
	kalite/main/api_views.py
	kalite/main/views.py
	kalite/settings.py
	kalite/templates/video.html
	kalite/utils/internet.py
Tweaks and commenting to address mplayer code review.
Use getattr syntax for USE_MPLAYER setting, to allow overriding.
Add name to launch_mplayer api url, so it can be reversed.
Fixes to mplayer thread launching.
To prevent multiple mplayer instances, throttle the launch clicks.
Fix the error with exercise description and added a test class for all urls data structure.
saving local changes
save tests
Now checks for all JS errors.
Update in names
Changed test name.
Added logging and linebreaker.
Added ability to specify in settings to only run fast tests.
Upgrade Selenium to get JS error detection to work properly in new FF.
Merge pull request #7 from jamalex/exercisedescriptionerror

Added ability to specify in settings to only run fast tests.
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into develop
Merge branch 'develop' of github.com:learningequality/ka-lite into mplayer_launcher

Conflicts:
	kalite/main/api_views.py
	kalite/main/views.py
	kalite/settings.py
	kalite/static/js/videoplayer.js
	kalite/templates/video.html
updating based on code reviews, more fully merging with existing changes