Introduces stock colors (primary_color, primary_dark_color, etc) to allow
overriding the colors via resource overlays.
Creates new colorSecondary attribute and updates switches to use theme
attributes for foreground/background colors rather than hardcoded values.
Some other mild color cleanup to make things more straightforward.
BUG: 28760785
Change-Id: I4deba962357217bdb2e08c08e8f83b9b57a683d4
8dd11327b6