Perform periodic transaction state updates

[dmitryn]

Description

After transaction message has been sent/received (with /send command) we need to periodically fetch transactions data (using etherscan API) to display transaction state to the user.

Now we run transactions state update after certain events like transaction message sent/received, user opens Wallet or user taps on chat message with transaction. If user doesn't perform any of these actions (stays idle for example), he ends up with an outdated state showing that transaction is still pending or missing:
#4851
#4865

Solution

After transaction has been sent or received, run periodic (say every ~15s) updater until transaction reaches certain number of confirmations (say 12 confirmations). After that point, we could stop the updater to minimize mobile data and cpu consumption.