Refactor push-notification related codes

This reverts commit 4d709b6e.

move raix-pushSetUser to SessionObserver. Because CurrentUserObserver is called back by "activeUser" subscription. not always logged in.

Improve login screen

Push notifications using the Cordova plugin code

fix login screen not to be refreshed onResume.

fix the issue that RealmObjectObserver's callback is called repeatedly

Uses black color (easy to tint later)
Fixes tinting in the message action selector