Rearrange collab titlebar items to avoid movement of the toggle contacts button

* Replace username in titelbar with a `...` user menu that shows
  the current user name and contains a sign-in/sign-out button.
* Move the '+' (toggle contacts) button back to the right side.
* Move the collaborators back to the right side.
* Move the share/unshare button to the left side, beside the project title
* Only show the share/unshare button when in a call.

Cargo.lock

@@ -1257,6 +1257,7 @@ dependencies = [
  "client",
  "clock",
  "collections",
+ "context_menu",
  "editor",
  "futures 0.3.25",
  "fuzzy",