join channels (#3082)

Release Notes:

- Clicking on a channel in the sidebar will now join the channel and
open the notes
- If you join a channel that already shared projects, you will join the
projects automatically and follow the host.
- Clicking on the current channel in the sidebar will re-open the notes.
- Chat can now be accessed from the right click menu of channels.


- (probably not worth mentioning) Various improvements to hover states
and tooltips in the collab ui; and if you click on a channel while in
another call, confirm before switching.