This commit supports displaying pinned events.

Type: add

CCBUG: https://iron.lily-is.land/T90

Verify unit tests pass. Pin some events in a room using a client that supports it (e.g. Fluffychat). Go to that room in kazv and verify "x pinned event(s)" action appears on room page. Click on that action and verify you can see a list of pinned events.