Unified Pay Method using "What am I looking at" #359

This Mutiny crate could be super useful for simplifying our send UX:
https://github.com/MutinyWallet/bitcoin-waila
We can just let users enter whatever they have. We can integrate it into a unified pay method, and then filter out anything starting with rgb: to automatically pay RGB invoices.
Then our wallet won't need multiple buttons, we can let the wallet figure it out with a unified text field.