Use V3 Onion address format exclusively in all user-facing contexts

[yeastplume]

In the 3.0.0 release, there is a bit of inconsistency whereby some commands accept a wallet's address as a raw public key whereas others use the v3 Onion address format. In retrospect we should only be presenting one format to users, not both.

For the 3.1.0 release, we should try and use the v3 Onion address exclusively wherever we can, which will include

• When specifying payment address manually on the command line, the user should be able to input an onion v3 address, not a raw key
• When retrieving addresses for the wallet, the user should only be shown the ov3 address
• When showing/exporting payment proof only the ov3 address should be used.

The slate format should not be changed for this, only user-facing instances where the address is displayed

The JSON-RPC APIs should be modified to accept either/or in init_send_tx via a custom formatter.

[yeastplume]

Done via #309