Convenient Coin APIs

[AlicanC]

having a helper method, either bound to provider or wallet, that encapsulates the fund transferring process (finding spendable coins given an amount, crafting the send TX, etc), like wallet.transfer(to, color, amount) or provider.transfer(from, to, color, amount)? Transaction signing would be also done out-of-the-box if transferring from the wallet struct (signing methods already in there).