Incoming transaction push notification and notification inbox

[packetstracer]

This is a feature that other wallet apps include and I think would be very useful.

Problem:
You cannot know when you've received some kind of transaction, the only way to find is go wallet by wallet looking at the transactions list trying to identify if the transaction is the one you're looking for.

Solution:
a) Push notification: this one is the most effective, because the user does not have to enter the app to know that a transaction has arrived to it's wallet (some users may not open the app for days/weeks).

b) Notification inbox: this one is good too, you enter the app and can see the unread notifications since you last visited the inbox. It could be used for other notifications, such as app updates, mantainance messages, voting proposals, etc.

Info to show:

• Tx type (received, vote proposal, announcement, etc...)
• Amount; tokens amount if any
• Memo: description/detail inside the transaction memo field
• Sender address: sender address of id