Set developer name to Khan Academy away from Brian Bondy

Test Plan:
- None
Add support for using the YouTube player

Test Plan:
- Test everything relating to videos
Add missing dependency for youtube api

Test Plan:
- None
Add support for loading indicator while video is loading

Test Plan:
- None
Update topic trees

Test Plan:
- None
Update youtube api files

Test Plan:
- None
Disable youtube player support until a workaround for the api bug is found.

I'd rather not do backouts for this work because there's a lot of good
video refactoring that happended to support multiple players.

Test Plan:
- None
Disable functionality if the APIs aren't available

This is in preparation for getting on the desktop ap store and android
store.

Test Plan:
- Make sure items are gone in desktop browser for downloading and
  sharing
Merge branch 'master' of https://github.com/bbondy/khan-academy-fxos into docs