Dynamic category expand/collapse

[MPArnold]

Function provided by a single new Class that may be optionally deployed from user's PreferenceFragmentCompat. [ No changes to core! ]

Had to clean up settings.xml - mostly to add keys for root PreferenceScreen and all PreferenceCategory. Forced by latest design editor to add full path for custom preferences.

Sample app updated and tested.

Please enjoy

[MPArnold]

Document sample app with instructions on how to request visibility of only a specific category or preference.

[MPArnold]

Added interface and documentation to allow user to suppress or override default scroll action.