Add a unique identifier to each notification

[kaivansanghvi]

Problem: If a user gets multiple notifications, say five, without a unique identifier(which is currently defaulting as 0, on android), only one notification will show up on the system tray. When user clicks on the notification being displayed in the system tray(which will be the 5th one, since that came last), it will open up the first notification that was received. Apparently it happens because Android internally queues up the notification in the order it was received.

[kaivansanghvi]

#126