UX: stop presence indicator hop, space consistency (PR #12797)

This eliminates the page jump that happens when presence indicators appear below a topic by reserving some space for them (may have been a regression that I caused recently?).

I also cleaned up spacing of items at the bottom of topics and fixed a consistency issue with the slow mode delete button.

Before:

After:

GitHub

Another one! :rocket:

Thank you!!! :blush:

may have been a regression that I caused recently?

It isn’t! :smiley: I recorded this gif as a todo in May 2020:

Kapture 2020-05-28 at 10 44 42