Add Renew command

[buffrr]

This PR:

• Makes the recipient field optional for transfers through RPC re-using the same script pubkey if not specified.
• Add a renew command to the wallet

Renewals "move" the space with changing any details so that messages signed with signmessage will remain valid. Of course, users can still rotate their keys by using the transfer command.

Using space-cli, you can renew like this:

space-cli renew @bitcoin