wait for confirmation of transaction

[marc0olo]

we need to introduce a way to wait for the confirmation of a transaction. related information here:

• https://forum.aeternity.com/t/aepp-sdk-python-does-waiting-for-confirmation-guarantee-that-transaction-is-on-current-chain/5857
• Wait for confirmation does not checks for forks aeternity/aepp-sdk-python#349

currently we e.g. don't provide the possibility to wait for a certain amount of keyblocks for the tx being mined.

I guess we should handle this asynchronously.