Stronger Semantics Around Sign Up "Steps"

[cyon1c]

Currently adding paid sign up options at the beginning of the process. The set of signup steps is currently: { phoneNumber | confirmPhoneNumber | username | email | checkYourEmail | finish }. While the process is relatively simple and straightforward now, it seems that it could be problematic as we add more, ie paidSignUp.

[gl2748]

I think this does that: Essentially the single source of truth for signup steps https://github.com/steemit/faucet/blob/master/src/reducers/app.js#L21-L30