Move 'display' to base

[ndelangen]

I'd like to use S and have it display-block. Currently I add style={{display:'inline-block'}}.

The Image component has a prop to tweak it's cssdisplay-property.

Maybe S should receive the same ability?

Either through adding it specificly to S or by moving the display prop to Base.
I think the latter makes sense.

I haven't made any contributions to spectacle before, but am interested in adding/tweaking this. Would you be interested in a PR, and if so which solution would you prefer?

[kenwheeler]

I'm going to remove prop based styling in favor of style tag/styled-components/glamorous type styling, so Base is going away