Comment 7 for bug 1671095

I actually believe we have most of what we need in here:

https://sites.google.com/a/canonical.com/apps-and-platform-team/8-shell/indicator-reveal

The only (I think) unanswered question is what to do with hidden indicators.
Should they be always visible when there's space available?
What if there is not enough space?
Auto-scroll similarly to the launcher?
Maybe they show up on mouse hover?