Deprecate all external Style Class APIs

[wpkelso]

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.

[danirabbit]

I think this is a good ideal but unless we implement our own buttons, for example, I don't think we can achieve it 100%