Beginning of a first pass at simple wallet functionalities so
Grin can be used to author transactions. We introduce a
receiving server, to be at least able to build coinbase outputs
that can be used by the mining daemon.
Present:
* Coinbase receiving API.
* Command to start the receiving server.
* Beginning of a transaction sending command.
* Improvements to the REST API abstractions to support the above.
Still to do:
* Change to the miner daemon to use the receiving server.
* A command line sender.
* API to receive any transaction (not just coinbase).
* A command line receiver.
Beyond that, HD derivation and seed generation are very simple
so far and almost certainly insecure. Just for testing for now.
Allows for custom operations associated with POST requests under
the main resource path. For example, in addition to POST on /user
to create a user, allow easy support for /user/login and
/user/logout.
