Collapse membership changes across day boundaries.

**Is your feature request related to a problem? Please describe.**

I'm always frustrated when I go to a quieter room, and have to wade through pages of membership changes before I can find the most recent actual content in the room. This is particularly frustrating if you click on the room after reading its room preview, and expect to see the message in that room preview, but instead see a page of other material:

^ This is on EW, but I think EI/EA have it too, hence filing on element-meta.

The problem is caused by the fact that we don't collapse membership changes over day boundaries, only within the context of a single day. So if a room is idle for multiple days, the changes stack up.

**Describe the solution you'd like**

Ignore day boundaries when collapsing events.

**Describe alternatives you've considered**

Hiding memberships entirely, as Discord does - or collapsing them much more aggressively somehow (little affordances in the margin or something?)

That said, in the example above, all the membership changes are profile updates. Perhaps we could just show the most recent update by default and hide the intermediary ones? The semantic info they provide is useful though.

**Additional context**

I haven't filed dependent issues for EW/EI/EA, so these'll need to be filed if the product gods smile on this issue.