THE BIG MERGE, part 2: magfest 8.5 branch into main branch

WIP, obviously this needs a ton of discussion/etc

Around end of July we merged the applicable parts of master-magfest85 branch into master.  Since then there have been a bunch of small fixes and other things that should go into 'master'.

There are also some changes here that should not go into master, such as fixes for groups/etc.

Once this merge is done, the 8.5 branch will go away and we will have only one 'master' branch for uber.
this is part of this:
https://github.com/magfest/ubersystem/commit/254f91a1f767faf7619948602d853556353f0987

"Make from_sessionized only add groups to Attendees
from_sessionized may be used more than once, so this is to prevent any
errors from adding a "group_id" to something that doesn't have a group."

should we include that?