feat: drain on-chain wallet

[bonomat]

Resolves #1538

[holzeis]

I guess it works, although I am not a fan of misusing the amount input field for that.

Maybe a drain button, that fetches the max amount that can be spent and sets it into the amount field would be better?

[bonomat]

I guess it works, although I am not a fan of misusing the amount input field for that.

Imho that's a defacto standard in Bitcoin wallets.

Maybe a drain button, that fetches the max amount that can be spent and sets it into the amount field would be better?

This is very hard to calculate in advance, you'd need to use the drain function first, then create the transaction, and then get the output's amount and return it back to the UI.

[holzeis]

@bonomat I forgot that this screen is also used for sending lightning. I think your changes will not work in that case.