Acceptance flow

This is the basic version of it with database additions, control buttons on admin (with the view user page cleaned up just a little), and the user-side confirm thing. Some text is placeholder like the doodle link.

As of first push, this doesn't automatically send emails. I want to get that working in the morning, but if it isn't done in time, we can still manually send them with mail merge or whatever, so this PR - once the placeholders are swapped out - can represent a MVP.
I wouldn't put the word doodle in the database column.  If we change interview scheduling software (very likely), what would be the plan?  Add a second column?  Do a rename and migration?  I think we should just use "interview_scheduled" and then it works for everything and is still specific enough for people to know what it corresponds to.