Loading the shielded wallet is stupid

[batconjurer]

Currently, the shielded wallet attempts to find a file and deserialize it, but of which are fallible. Upon failure, a default (empty) wallet is created. This is fine if the file is missing, but causes stupid shit when we've changed the wallet format and deserialize fails. Thus to unshittify the situation, we should do the following

• If the file is missing, use a default
• If deserialization fails, try to run a migration (this requires versioning shielded wallets)
• If deserializing / migration fails, error out explicitly