wrap all API calls with error catching, so all API return Json-based errors
update video_download
raise Http404, not return
Merge branch 'develop' of github.com:learningequality/ka-lite into safe_api_errors

Conflicts:
	kalite/securesync/api_views.py
updating formatting on video_download
Added basic Google Analytics tracking to the update page.
essentially re-applying commit dc1c4a01d020a822affe21aec77a4faa2335c4c7, to set id=slug
updating topic data to fix regression bug.
Redid update page Google Analytics to set variables via template tags.
Merge pull request #455 from bcipolli/id_vs_slug_regression

Id vs slug regression
making strings more i18n-friendly, being careful to only display a single error of a single type.
fixed bug in display of API errors in video_player.js, safer error handing for 403 error in video_download.
Merge pull request #456 from jamalex/ga_tracking_on_update_page

Added basic Google Analytics tracking to the update page.
Looks cool, thanks!!
removing debug-only text.
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into safe_api_errors

Conflicts:
	kalite/templates/video_download.html
Merge pull request #439 from bcipolli/safe_api_errors

Safe api errors
Resolved merge conflicts, removed debug-only assignment, opened issue #461
changing _new to _blank
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into api_error_cleaning
fixing bug when json response returns empty.
Merge pull request #436 from bcipolli/raise_not_return

raise Http404, not return