First pass at new FolderIcon visual treatment

-> Modeled as a set of items around a circle
-> Modulate the radius and icon size as number of items grow
-> Clip the icons by a circular clip aligned to the background drawable

Remaining issues
-> Probably want to move to a programmaticly drawn circle + shadow
-> Anti-aliasing of the clipped region will need more attention
-> Need to animate all items in the preview as it changes (this
   wasn't required before)

Change-Id: I678ec605f6c8a34e9d7e4aec4e9583e36a9ef394