Moves the logic requesting the forward swap into the TxEditor so it can
use the open transport and doesn't have to reconnect to the relays
again.
Also disables the "Preview" button in the TxEditor when the transaction will
send change to lightning.
This should prevent the user from saving the transaction to history and
broadcasting it later or exporting it and broadcasting it through some
external way.
Broadcasting needs to happen directly after the TxEditor so we can send
the second rpc call to the swapserver and await the incoming htlcs
before broadcasting the (funding-) transaction.
f321x
1b28e6bf73