Remove non-functional style from the core grid -- pull them out into an examples.css

[gabrielmontagne]

It seem that even though we tried to keep the selectors "light" on the vanilla grid -- the grid is still hard to style and the stuff that we added so that the examples wouldn't look too sterile and the grid would look good "out of the box" still pop from under the real styles that apps layer on top.

Also, it looks as if those styles were created by a developer. Perhaps they were? :^/

It'd be good if the grid without styles functioned fine but didn't look like anything.

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Also, styling row and cell divisions is unnecessarily hard because we use both on the vanilla stuff.
Might be a good occasion to see how this could be made easier?