Cannot use Multiple Utxos on Bitcoin

[gagdiez]

In Bitcoin, the balance of an account comes from all the unexpended inputs on their account

Our current implementation only allows creating outgoing Bitcoin transaction using the utxo with the highest value

This becomes a problem if the user wants to use their whole balance, or balance that comes from more than one incoming transaction

What needs to be done

• Order the user's utxos by highest to lowest
• Create a batch transaction, asking to sign all the utxos separately
• Transform those signatures into a single bitcoin pst

[PiVortex]

Maybe #49 will fix this, multichain-tools may have support for this