[DA] Collab and quick edit mode in preview

[rofe]

• If the sidekick is open on a preview URL and the underlying content source of the current resource reported by the status call is DA:
  • Enable live collab view, i.e. show other users' cursors, selections and changes
  • Add secondary actionto the Edit button, showing a menu with a Quick Edit action on long press. Click action remains as is.
  • Quick Edit enables in-place editing
• Closing the sidekick returns the page to its static original state.
• Opening the sidekick again restores the previous state