privacy Guard enhance app logic
This commit changes the following

- do not show apps signed with the plaform certificate at all
  (like settings, systemUI, android system etc)
  IMO the user should trust the android signed apps to be save and this will
  prevent weird behaviours user can get when they activate it on this packages
  all other system apps (like calculator, browser) and all which are not signed with
  android key are not effected.

- to go inline with AOSP disable the checkbox in detail app screen
  for built in apps

cheers

SlimRoms

Change-Id: I12b5522f6e58047173778381fb7290bb1c71bab3