New track changes UI
This should be similar to the second option in #39 (closed).
More specifically, let's put the controls for track changes in the main toolbar.
The user should be able to navigate to the next or previous change, as well as accept or reject it from the toolbar.
The tools should be disabled when:
- Track changes feature is off
- Tracked changes are hidden
- The user doesn't have the appropriate persmissions to resolve a change
- The current selection does not include a change, or includes more than one
The line height should come back to normal.
On a second iteration, we should probably hide the controls instead of disable them for the above scenarios.
@julientaq might be worth it to start thinking of a design for this.