Settings: setting to enable/disable translucent decor (2/2)

using aosp code for enabling both lockscreen and home screen decor:

  - add default setting, overrideable in overlays
  - retain aosp config for functionality

Change-Id: Iee6e5d405056a9b242f75c759bf5f04fd2b59455
Lockscreen Style: alpha sliders for all color picker options

Change-Id: Id48996db30ad284901f8bd266604e1a16c6426cc