SystemUI: Add double tap to sleep gesture

 Change-Id: I4c54718e8ec8774677d13917b3a7ffa3b4b18cb5

Change-Id: Idcf0d72736e3302a57a91649d51009103f7b0538
base: MediaScanner behavior on boot (1/3)

Lets you enable/disable/ask (with a notification) media scanning on boot.
Can speed up boot and reduce initial boot lag from MediaScanner

Change-Id: I634ae96b1dcb493b966b4653589cd97523b63da7