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
Updating update language interface to align data better, define lang packs.
Merge pull request #1172 from aronasorman/1118

Allow upgrading of language packs, use sprintf.js, and some refactorings in update_languages.js