* Add ability to configure FCM_API_KEY and FCM_POST_URL
* Delete APNSDevice and GCMDevice instances when unlinking the mobile app backend
* Add a simple FCM relay endpoint
* GCM -> FCM
* comment
* add permalinks list to internal API alertgroup view
* add user's name and full avatar URL to the user view
* make avatar_full_url a property
* fix tests
* fix user connection criteria
* move mobile notifications to a separate backend, remove critical notification
* remove outdated mobile app code
* MOBILE_APP_PUSH_NOTIFICATIONS_ENABLED -> FEATURE_MOBILE_APP_INTEGRATION_ENABLED
* create error log if no devices are set up
* move mobile auth related code to the mobile_app Django app
* move mobile auth related code to the mobile_app Django app
* move mobile auth related code to the mobile_app Django app
* fix typing
* add GCMDevice todos
* add user connection capabilities
* add user connect/disconnect to the messaging backend
* move APNS endpoint to mobile_app Django app
* restore critical notifications
* support hackathon app
* tweak migrations so mobile app auth tokens are preserved
* reuse notify_by IDs
* use mobile app template to render push notification
* add GCM/FCM (Android) support
* fix unlink user
* logger.error -> logger.info
