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.
initial demo of downloading data from KA into a facility user account
fixing max bug
make things run through settings and stored in a session object.
intermediate checkin to share code with central server.
pushed all oauth / api logic to the central server; now distributed server just exposes a simple callback with strong assumptions on the data.
adding missing central urls. improving debug info.
restoring escaping on callback, don't allow GET requests
allowing ACCESS_TOKEN to be cached, adding HACK to get playground to work
Merge branch 'khanload' of github.com:bcipolli/ka-lite into khanload
Merge remote-tracking branch 'origin/control_panel' into khanload

Conflicts:
	kalite/central/urls.py
	kalite/coachreports/views.py
	kalite/main/urls.py
	kalite/settings.py
	kalite/templates/coachreports/student_view.html
created a student 'account management' page; moved green button (and student coach report contents) into it.
fixing up data collection.
re-enabling UI functions for control panel