Early crew doesn't always go on rideboard/tentboard

Early crew gets people in the log cabin, and also doesn't put themselves on rideboard because they leave early. Allow people to add themselves to earlycrew, have a tab with a list of early crew members (so Potter can get a headcount), and the people on that list will NOT be required to be on rideboard or tentboard

Start by tracing the existing rideboard and tentboard flows alongside the current crew and log-cabin handling. Add self-service earlycrew membership and a headcount tab, then verify that early crew members are not required to appear on either rideboard or tentboard.

Written by the indexing model from the issue text.