Changed version to APP_PREVIEW
Factored out generic extraction code
Added Apps link in main menu
Make default locale available to app code
Implemented basic app listing
Changed background globally so footer blends in
Basic app listing
Server- and client-side API for working with files
Handle all errors with bad zip files
updated changlelog
Merge branch 'apps'

Conflicts:
	librarian/lib/downloads.py
Updated changelog