Add checkbox to checkin process to indicate staff/volunteers have signed the waiver

[RobRuana]

A signed staff/volunteer waiver is required for MAGWest, because of specific California employment laws. The checkin form should have a required checkbox for any staffer/volunteer to indicate they've signed the waiver.

[RobRuana]

This could maybe be implemented in the main uber repo, with a config option to turn it off/on. Or we could just do it in the magwest repo, make it a little easier.