Fixes spacing of color options in wallpaper picker.

This eliminates overlap and clipping of color option backgrounds, and
also adds vertical spacing between rows if the options spill into a
second row.

Fixes: 227690986
Fixes: 240448797
Fixes: 231414521
Test: Passes TreeHugger
Change-Id: Ia3a2a1c7ae27d9afdf446226c83845be2221f432