Adding customizable background colour support.

Adding customizable background colour support.

Also changes how sub-styles are created: copies the modified properties
like e.g. fullscreen from Material. Previously most sub-styles
inherited from their material counterparts and updated just some colors.
The new approach should be more stable wrt changes in device default
theme. It would need updating when Material is updated but these kind
of properties does not look like it would be updated often.

Bug: 31459804
Change-Id: I78862bf33ca3dac586ad0a25f17bf8c0008a1dd0