Change default_wallpaper (Credit to Alexandre Lionne)
Implement Dynamic System Bars [1/2]

This commit implements DSB. Simple as that.

All the changes:
- frameworks/base (I3bc7102b2139fd1fa3de22aac096bd2a75bde878)
- packages/apps/Settings (Id2b105dfb3faf3cad74d0fa0dc33d01f6b71a853)

Change-Id: I3bc7102b2139fd1fa3de22aac096bd2a75bde878