fixing decorator bug and other bugs long fixed ago
remove empty start callback
use sprintf.js
refactor -- place both adding installed languages and showing
installable languages into a single function
cleanup on some use of sprintf
factor out code that starts language pack download into its own function
solve issue #1118: Add upgrade link if a central server version is higher
Merge remote-tracking branch 'refs/remotes/upstream/release-0.11.1' into 1118

Conflicts:
	kalite/templates/base.html
Retrieve network adapter IP addresses, and show them on easyadmin page.
Merge branch 'release-0.11.1' of github.com:learningequality/ka-lite into determine_ip_addresses

Conflicts:
	kalite/main/views.py
Use get_ip_addresses() in setup command, to show full list of IPs.
Updating JS url to match API
disable gzip in nginx
Merge pull request #1175 from gimick/no_gzip

disable gzip in nginx
Add "stage_status", to track (and report) errors and cancellations.
Use stage_status for better video updates (better error reporting)
Updating update language interface to align data better, define lang packs.
fixing small bug in update
Merge pull request #1172 from aronasorman/1118

Allow upgrading of language packs, use sprintf.js, and some refactorings in update_languages.js
Merge branch 'release-0.11.1' of github.com:learningequality/ka-lite into smoother_updates