As discussed on #electrum yesterday.
Increase change gap limit to 6.
Choose the next unused change address, if any, otherwise pick
one at random from the gap limit.
Fees should be recalculated when send_from changes.
Fees should be recalculated when editing fee preference, but
only save to storage when leaving the fee per kb widget.
No need to emit a textEdited signal; the widget does that already
(with the effect that we used to call update_fee() twice).
Whilst it's not a good idea to have two electrum instances
open on the same wallet, we should avoid throwing an
exception. Also note how the old code's handling of the
exception (caused by both renaming the file almost at the
same time, rather than a non-POSIX system not supporting
the atomic rename) can lead to the wallet file being lost
enirely because os.remove(self.path) succeeds and the
rename of the temporary no-longer-existing file then fails.
A couple of changes
1) Old electrum wallets seemed to save labels in latin1, when you call json.dumps on line 83/84 it fails silently, which causes the label import to fail. Whenever electrum saves, it then overwrites your default wallet with no labels - essentially deleting all your labels. The solution to this is iterating over all the labels for old wallets decoding anything that fails to unicode() as latin1, and then unicoding it :)
2) Failing to import data and then deleting it is bad. So I'm raising an exception to avoid data being lost.
The verifier will retain responsibility for verification, but will no longer
hold the transaction sets itself.
Change requires_fee to take a wallet.
Add new function add_unverified_tx()
Move get_confirmations() to the wallet from the verifier.
