Modify Group requests and join storage to use strings

[Acidity]

Joinable and requestable groups had significantly longer execution times for Group.evaluate prior to this change, as we were dereferencing the entire join_members and request_members lists from the database when all we needed to do was check if the user was in it. We switch to storing only the character names, which are guaranteed to be unique, and which doesn't require expensive dereferencing while still meeting all of our intended use cases (being able to easily check if a character is in the list).

Signed-off-by: Tyler O'Meara Tyler@TylerOMeara.com

[jboning]

Seems sensible! I'm going on faith that you've added .name everywhere that needs it :)

Can you add a note in the upgrading instructions about the migration? Then I will merge