Better info about transaction fees, make it easier to have the recipient to pay the fee

Sometimes we want the recipient to pay the transaction fee.

First: It is not clear in the UI who pays the fee. One can't tell from the UI whether it will be subtracted from the sent amount or from the remaining balance. It should be absolutely clear in the UI how much BTC will be subtracted in total and it should not require one to know the inner workings. This is not something that should be assumed from users.

Second: If we want the recipient to pay the fee, we have to simulate the transaction, see the fees that we would like to pay, then recalculate the amount to be sent to make room for those fees. This could be made easier.

So, it would be nice to:

• Show the total amount to be subtracted.
• Let users modify the amount to be sent as well as modify the fee
• Make amount and fee to be copy & pasteable. So they can be copied to a calculator.

Even we could have an "I pay the fee" or "the recipient pays the fee" selection that modifies how the total transaction and the amount to be sent are calculated, but this may escape the scope of Electrum.

Start by reproducing the transaction-fee flow in Electrum's UI and compare it with the attached screenshot. Trace how the sent amount and fee are presented and calculated; the work is done when the total subtraction is clear and users can adjust and copy the amount and fee, with recipient-pays behavior defined if it remains in scope.