[WIP] Button for Stream Messages, towards Private Messages Sidemenu.

[plugyawn]

What does this PR do?

Towards a fix for #1197. Adds a StreamMessage total in the top left.

WIP PR, accidentally wrote it on top of some pre-existing code -- I'll be updating the PR asap, just wanted to know if it was working properly.

Tested?

• [x] Manually, but there are errors.
• [ ] Existing tests (adapted, if necessary)
• [ ] New tests added (for any new behavior)
• [ ] Passed linting & tests (each commit)

Commit flow

Notes & Questions

• Need to check if the PMs indeed are not appearing in the narrow.
• Need to fix the counter, seems to be not updating.

Interactions

Visual changes