Need redis for CI now

fix CI

New debian stable doesn't have postgres 11

invites table

Table to store invite codes and their status.  Stores who make the code and
when, who used the code (if anyone has used it yet) and when, and the code
itself. Codes are single-use so once used_by_id is set the code cannot be used again.

plan_log uses a tsrange instead of two timestamps now

This is honestly just more correct, but also allows for easy checking of
non-overlapping ranges, which we now do.

ci