Clear popovers on stream narrows

[showell]

If you narrow to stream A and open its popover menu, then click on stream B in the sidebar, the popover for stream A still sticks around. Generally, we solve this by calling popovers.hide_all(); at the start of various UI actions (or at the start of trigger event handlers). This should be an easy change, with the following minor challenges:

• We want to avoid having lots of calls to popovers.hide_all() in our code, so we should be thoughtful about the best place to put these.
• When you're manually testing this fix, you should try to uncover similar bugs by doing things like narrowing from the recipient bar, searching, opening up other menus, etc.

[jacklqiu]

Don't know if this is related, but if you press the down chevron and scroll up or down. The popover doesn't exit.

[timabbott]

@540KJ I'm not sure I understand; can you post a screenshot or brief video?

[jacklqiu]

As you can see, the popover doesn't belong to (no topic), but rather lorem ipsum. Obtained through opening popover and scrolling up.

[timabbott]

Ahh, OK, yeah, that makes sense. Probably a totally independent issue from the clearing bug; can you open a new issue with that screenshot?

[timabbott]

I think this was fixed by #3088.