Preliminary work on Material Transitions

Preliminary work on Material Transitions

-> Early exploration of AllApps Hero transition with
   circular reveal
-> Stripping a bunch of dead code from AppsCustomizeTabHost
-> Moved background scrim to DragLayer
-> Removed "SMALL" state from workspace: replaced with
   NORMAL_HIDDEN and OVERVIEW_HIDDEN. This is mainly to
   reduce the overall usage of the z-space model between
   allapps/widgets and workspace. There are vestigial
   remains of this model, mainly due to the overview
   mode, and a bit for spring-loaded.

Change-Id: If2302a24394f0ec66621f01ffa2fc4934aa10c3f