Settings: MediaScanner behavior on boot (3/3)

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

MY NOTE: I didn't cherry-pick it due to different files from other ROMs

Change-Id: I06499ab5bd6db286470d3d7ef00d269a31a2ae38

Conflicts:
	res/values/pa_arrays.xml
	res/values/pa_strings.xml