Refactor styles again, this time trying to seperate the more
layout-specific attributes so that layouts become more re-usable.
This also updates the naming conventions of styles.
Instead of using @color/background directly, use ?attr/colorSurface
so that changes can be made to the theming easier. This also
resolves some more minor issues regarding certain widget's
backgrounds.
Do two things to the margin and padding system:
- Remove the redundant padding/margin dimens and replace it with a unified "spacing" dimen namespace
- Make most margin and padding dimens follow the divisible-by-8 rule in material design
