Closes#677
- Previously when keychain wanted to do wipe wallet had to do it on it's
own. Which isn't good. Now wallet can simply call
`synchronizer.wipe()` and it's done.
- This change brings support for wipe. `Synchronizer` has new method
`wipe()` which takes care of everything. All the database connections
are closed. Databases are removed. `InternalSyncProgress` is reset.
Change condition when wipe can run