Deprecate all external Style Class APIs

Many of our public style classes are targeted toward a few widgets, or have some general parameters we tend to use by default (`CARD` doesn't work well if the element has no margin).

Instead of having developers apply these styles manually, I propose we deprecate exposing all existing style class constants externally, and control their application via properties on subclassed widgets instead. Ideally, this leads to more concise end-developer code, and we can give away more defaults for free.