Implement divider UX interactions

- Update visuals to spec
- Divider lifts when touching
- Implement basic version of snap points and animations
- Implement touch conflict behavior: If touched around 48x48dp
area around the handle, the divider handles all these touches.
If touched outside of the black background divider, touch goes
directly to underlying window. If touch on the black background
divider, touch is considered slippery and thus the window in
which the touch trace moves gets the touches.

Change-Id: I0307c191ae032672c4b73d439c23cf9833d3fce6