[Android] [URBNG-366] Add "Game over" functionality in application

Short description: User can now see notifications in application. Every ~10 seconds (this time can be changed) user is able to see one of the following notifications:
- gameNew
- gameEnded
- gameOver
- taskNew
- taskChanged

Long description and changes made:
- lines 317+ in NotificationHelper.java are just mock methods of this class to simulate that new notifications are available. Most of the job was done already.
- lines 55-155 in NotificationHelper.java and file NotificationHelperTest.java adds WebServer functionality to NotificationManager
- added method "equals()" in classes: Task, UrbanGameShortInfo, UrbanGame to reduce code repetition
- added method isApplicationRunning() in UrbanGameApplication class. I needed it to terminate a Thread (mThread in NotificationHelper class), beacuse when app normally exits the thread is not terminated with it
- NotificationHelper class is now launched from MenuActivity so this class can run from the moment when application starts

I made this pull request so user could be able to see that notifications work. I am also waiting for "[Android] Notifications completed" pull request to use some if its code.