Unify next / prev page hints for drag and drop across devices

-> Eliminate the white bgs on tablets during drag (issue 15880213)
-> Add stateful (active and rest) next / prev page hints (issue 15937059)
-> Fix recent regression which allowed overscroll in custom content area

Change-Id: I1198dc88ca8570cb9e1afd3ca939be06a8dea92e