add Cordova PushPlugin (https://github.com/phonegap-build/PushPlugin)
updates for push notifications

1. get and update the device ID
2. react to notifications
read "GCM Sender ID" from strings.json
Merge branch 'feature/push-notifications' of github.com:usersource/anno into feature/push-notifications
Fixed "Server URL" dialog initialization issue
Merge branch 'feature/push-notifications' of github.com:usersource/anno into feature/push-notifications
[iOS App] Made changes for making push notifications work on iOS
Merge branch 'develop' of github.com:usersource/anno into feature/push-notifications
[GAE Server] Sending title with Android push notification message
Merge branch 'feature/push-notifications' of github.com:usersource/anno into feature/push-notifications
[GAE Server] Using UserAnnoState for 'My Activity'
[GAE Server] Catching exception in 'anno.mystuff'
[GAE Server] Added API for getting list of user's favorite apps
[Android] Added option to show push notifications in big view
[GAE Server] Added option to clear device info from user datastore
[GAE Server] Fixed minor bug with datastore migration script
[GAE Server] Corrected push notification message for 'comment'
[GAE Server] Added API to update AppInfo model
[GAE Server] Code refactor
[GAE Server] Catching exception in 'convert_document_to_message' while getting Anno