Only require the user to input the passphrase once, unless creating
a wallet.
Should they mis-enter the passphrase, they will be warned Electrum
couldn't pair the device, and when they actually need to use it
they will be prompted again.
Fixes#1672
Move session timeout from wallet to config
Prevent timeouts whenever a device operation is in progress
Move timeout job from each plugin to device manager
Tell the user and ask if they want to try again. If they
say no, raise a silent exception. Apply this more friendly
behaviour to the install wizard too (see issue #1668).
Only warn about watching only once given a chance to pair.
Failure to pair makes watching-only and warns.
In error message to user, distinguish between failure to connect
and failure to pair.
ThomasV
Neil Booth