Add registration management in-app

[merlinorg]

Trying to coordinate through email, wordpress, forum and discord is frustrating. People have different names in every system, use multiple email addresses, have multiple strava accounts.

The site should be involved in the registration process to the extent that it knows everyone who is registered, can let people see their registration status, can let people see whether they have miles recorded or are waitlist bound, can demote themselves to friend-of, etc etc. It can also then manage the waitlist so it's less crazy trying to find people to add to teams.