Hide the stack education view when user taps

This was only hiding if you interacted with the bubble, now it
will hide if you tap anywhere.

Also makes sure the bubbles are ordered above the education.

Bug: 189225662
Test: manual - wipe device, get first bubble, tap anywhere other
               than the bubble & observe that the user education
               fades away.
Change-Id: I3750ca79de717e81492070b38d1af0518f1a7a3f