Add preference for enabling root access

  - Requires support in su binary and adbd
  - Root access can be configured to use ADB only, apps only, or all
  - Root and adb enabled by default
  - Fix losing root access when flashing custom kernels

Change-Id: Id88edfc4bd7eb67e1f04c02922553a73c8c4766f

Conflicts:
	res/values/gummy_arrays.xml
	res/values/gummy_strings.xml
	src/com/android/settings/DevelopmentSettings.java