Show-before-send currently asks for the password
and creates a signed tx before showing anything.
This is a little unnerving as you can't see what
you're being asked to sign.
This patch does a few things:
- Adds a description label to the TX dialog
- You see the tx before being asked for password;
that is only requested on pressing Sign
- in show-before-broadcast mode, the Send button
text is instead "Show...". Hook up this button
text change to the prefs dialog too.
- Remove many redundant imports. In particular
PyQ4 is checked in main_window.py so no need
in tx_dialog too.
Note I had to remove disabling of the Sign button,
because if the user presses "cancel" nothing will
re-enable it.