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.
selecting urlconf conditionally; remove obsolte urls.py
full clean before signing, to make sure what we sign is the data that we'll keep.
fixing bug in format_name logic; now can accept objects or dictionaries.
Merge remote-tracking branch 'jamalex/mplayer_launcher' into khanloadv2
fixing url reverse lookups for renamed url
simpler user experience for registration; now no recurring refresh, window to close--just a callback url.
central-server-side of redirect.  This also forces the sync to run, with no confusion to see that the device has not yet sent sync data to the central server.
Merge branch 'redirect_to_force_sync' of github.com:bcipolli/ka-lite into redirect_to_force_sync

Conflicts:
	kalite/securesync/views.py
adding a command-line utility for executing common testing functions
missing delete function on config.
Merge branch 'redirect_to_force_sync' into khanloadv2
Merge remote-tracking branch 'origin/katest_tool' into hth
small bug blocks purgatory