Summary:
This diff adds multiple selector UI on layout plugin, which shows up when there are more than one component at a touch.
This UI allows user to do similar thing to element inspector. Expanding functionality on main component will be added in next diffs.
Reviewed By: mweststrate
Differential Revision: D21214899
fbshipit-source-id: 5c9cae93122cc4f7c326ccd0878d2b9dddebf62b