[framework] Integrate new quantizers

- WuQuantizer, CelebiQuantizer, and WSMeansQuantizer for implementing
Celebi's weighted squared means algorithm for color extraction
- CentroidProvider interface added; allows easy switching of what
colorspace/dimensions is used for clustering during color extraction

Test: Run, switch between a bunch of wallpapers,
switch dark/light theme, repeat ad nauseum. Unit
tests in separate Android Studio project hosting
the library pass, will add those to Android in separate CL.
Fixes: 180641035

Change-Id: I0fc60a134f411845dab9d6c7d8553907849d0f8a