ARMORY-118 - Import & export of root public keys (watch-only wallets)

Fix multiple bugs.

-Wallets couldn't be restored after commit
a767e9abd928566f9f160a1c6f389878508b534c.
-Wallets didn't have their addresses restored.
-Wallet address restoration didn't include a progress bar to let people
know work was being done.
-Full wallets could be overwritten by these watch-only wallets.