Refine color overlay attributes

- Clear OVERLAY_COLOR_INDEX attributes when wallpaper changes.
- Update OVERLAY_COLOR_BOTH to know wallpaper color is for both
  home and lock screen or not.

Bug: 186194356
Test: atest ThemeOverlayControllerTest
Change-Id: I76a0ce6c7e8455d21a890f7ac44e8ffe90dcb367