Shadows - apply breaking points

[lars-lindstrom]

Shadows are a great feature, and the choice of sizes are fine. But I think breakpoints are missing. While shadows look great on larger screens, the tend to have less use on smaller devices i.e. cell phones. Thus a shadows-none, shadows-none-sm, shadows-none-md, shadows-none-lg, shadows-none-xl and shadows-none-xxl would be fantastisk.

[mdo]

Wrong repo, and this is accomplishable with our utility API.