Fix jank when switching themes

Turning overlays on and off takes time,
it also doesn't allow us to have fine control
over which view is using which theme.
Lock screen colors are now driven by themes.

Change-Id: I4b5db6234cafebbe8eaa952781c038370a11488b
Fixes: 63751714
Test: Visual. Set wallpapers, unlock.
Test: runtest -x tests/Internal/src/com/android/internal/colorextraction/ColorExtractorTest.java
Test: systrace