Low battery warning policy (2/2)

Option to choose how low battery warning will be indicated
- Popup dialog and sound
- Popup dialog only
- Sound only
- Off

Change-Id: I6fa2c45301d37ca3086703bf1eddde12b45ba6f9

Conflicts:

	res/values/arrays.xml
	res/values/strings.xml
	res/xml/rootbox_settings.xml
	src/com/android/settings/Rootbox.java

Conflicts:

	res/xml/system_settings.xml
	src/com/android/settings/cyanogenmod/SystemSettings.java