fix the missing break...
works:
1.add a new "cache settings" category in settings view
2.add two options in cache settings (UI work only)
  - thumb quality
  - clear all records
3.fix the incorrect list preference values/default value setting logic
works:
1.implement clear all functionaltiy in settings view
2.make the palette list view reload data when the main view resumed, it
is not the best solution to refresh list view but could be the simplest
way to always keep the palette items in list view sync with data in db
3. remove the "dangerous" operation "clear all" from the menu opetions
in list view
Implement the function to tweak thumb quality based on the thumb quality
value in settings view