This is the settings part of the change for adding
support for accessibility service specific settings.
1. Added the first cut of a SettingsCheckBoxPreference
that is a CheckBoxPreference that optionally takes
an intent to be lauched as settings of the item
represented by the preference.
2. Updated the AccessibilitySettigns to use the
SettingsCheckBoxPreference.
Change-Id: If44262b8965c65620c6b8c252f8ef356eb0d95cf
6f0b4d8143