Use Forwardable for simple delegations

New signup: go to web to choose credit card

This step, if chosen, directs the user to the jmp-pay webapp to add a credit
card.  It includes an OOB element for use by user agents that can handle
that (possibly for webview embed, etc) with a note-based fallback as per XEP.
Once the user chooses "next" the code checks if they have actually added a card,
and if so continues to a yet-unimplemented step and if not repeats the
instruction to go to the web app.

Merge branch 'register-command-first-pass'

* register-command-first-pass:
  Add sourcehut CI
  Add Rakefile to run all tests
  Initial registration flow for Bitcoin
  Registrations that start on the web will have a tel selected already
  Helpers for doing Electrum RPC
  Add helper to fetch current BTC sell prices
  Allow skipping tests without being caught in pry

Initial registration flow for Bitcoin

This is the Bitcoin "happy path" where there is already a tel and a customer_id.
Gets all the way to generating a BTC address for payment and quoting an amount.
Stubs out flows for credit card and activation code as well, but does not
implement those flows.

TBD: after bitcoin payment comes in and jmp-pay activates the account, we should
come back here to actually buy the number, select a new one if no longer
available, etc.

Split logic out into testable objects

Rubocop clean. Good test coverage of helper objects.