Ref T7566. Prior to this diff, we had a broken mess in the "Messages" section. Now, "Messages" behave like rooms in that whatever is loaded at page load time is at the top of the list.
Additionally, refine "show more" behavior such that it simply shows the next X, but if there exists X + 1 then we have another "show more" that kicks you to application search. Theoretically, there are still corner cases where users are in a ton of rooms or a ton of messages respectively, but this feels pretty good.
Consolidates title rendering code so we always render the list of participants and no more "No Title".
Also remove the policy icons for messages consistently, helping to differentiate them from rooms at a glance.
