R1:25767096c931

Conpherence - implement join / view rules for rooms

Summary:
Ref T7585. This implements everything specified, with a few caveats

- since rooms you have yet to join can't be viewed in the column yet, the column view has some bugs and isn't expected to work.
- the room you're looking at is just pre-pending to the top of the "recent" list

Test Plan: made a room that no one could join. verified when viewing that there was no comment ui. made a room that others could join. verified folks who had yet to join…