migrating to central server API scheme.
adding response headers
using JSONP to get data from central server.
Merge branch 'subtitles' of github.com:dylanjbarth/ka-lite into subtitles

Conflicts:
	kalite/central/api_urls.py
	kalite/central/api_views.py
	kalite/templates/video_download.html
Merge pull request #2 from bcipolli/subtitles

Serving subtitle counts from central server