Split logic out into testable objects

Rubocop clean. Good test coverage of helper objects.
Currency aware

Look up the user's plan to find out what currency to charge them in.
Submit for settlement

We'd like to actually get the money, not just be allowed to.
Always show money with two decimal places
Only ask which card to use if there is more than one
Write initial buy credit command
Initial commit

Supports registering with backend SGX via basic iq:register.

Does not support data forms version with nice labels.

Does not verify billing or anything else yet, just unconditionally registers the user.