Misc updates to AccelerometerPlayActivity

- Fixes background image scaling
- Reduces number of particles for visual effect
- Misc changes to physics logic
- Use views instead of bitmap for particles

Additonal modifications by trevorjohns:
- Removed unused code
- Simplified duplicate calculations
- Updated minSDK to 11
- Updated targetSdk to 23
- Removed stale taget API annotations

Contributed by: Wojtek Kaliciński <wkal@google.com>

Change-Id: I104da4100ea0670ed5c06354ea71e37564a77752