Put DessertCase on a diet.

- store desserts as ALPHA_8, saving 75% of bitmap memory
- run DessertCase in its own process, avoiding bloating
  systemui every time the daydream or platlogo activity run
- lock orientation in DessertCase to stop thrashing around
  when the device is rotated

Bug: 10918599
Change-Id: Ia2fb0696b903ae355c75b53d3a0c45b70784d00c