use nicer with-syntax for multimedia zip
extract zip and media file iteration from DownloadMultimediaZip
add multimedia to offline install

implemented by refactoring DownloadMultimediaZip and then subclassing

this required moving a fair amount of code around to get rid of import cycles
add a local authority to media resources for offline install
put only the right profile file in .ccz

- exclude everything except media_profile.ccpr
- name that file profile.ccpr
Add missing import
limit offline install changes to >=2.13 apps

- only include a local authority on media resources starting on 2.13
- only include the offline install option in ui starting on 2.13 apps
- pull out all enable_* methods of Application that check for feature
  support into a separate mixin, and have these methods available to
  SavedAppBuild for use in releases page
improve wording for Android Offline Install feature
move offline android install ui into Download to Android
Only allow user to download to android if version >= 2.13.0
Removed unused code that should not have been committed
Merge pull request #3511 from dimagi/offline-install-multimedia

Offline install multimedia