* change all user-facing instances of addresses to a SlatepackAddress
* finish renaming get_slatepack_address + documentation
* get_slatepack_secret_key OwnerRPC implementation and test
* add owner api functions
* OwnerRPC functions + doctests
* add explicit slatepack API tests to exercise encryption
* update api function names to better reflect RFC
* addition of SlatepackAddress type
* complete conversion of ed25519 keys to x25519 and isolate conversion within libwallet
* refactor packing/unpacking of slates logic into libwallet and out of slate adapters
* println
