Settings: add safe headset volume and less annoying sound notification

Add settings for both features.

Change-Id: I8ab4f4b9ec320238b05ac51fb76ac24b93c37d37

Conflicts:
	res/values/cm_dimens.xml
	res/values/slim_strings.xml

	modified:   res/values/cm_dimens.xml
	modified:   res/xml/notification_settings.xml
	new file:   res/xml/slim_sound_settings.xml
	new file:   src/com/android/settings/slim/SoundSettings.java