Notifications cleanup.

Cleaned notification packages, removed unnecessary files, little fixes
and changes.
Notification skeleton

Created basic functionality for notifications.
Notifications mechanism completed

- Sub-task URBNG-361, URBNG-362 and URBNG-364 completed
- NotificationDiff sekeleton created
Merge remote-tracking branch 'upstream/android' into android
Pull-request fixes after remarks
Merge remote-tracking branch 'upstream/android' into android
Added comments
Merge pull request #92 from KamilLelonek/android

[Android] Notifications completed