Eliminate cascading margins on column

This is a more thoroughgoing solution to the namespace issue with
margin-right and left, but after discussion, it’s not clear that
cascading margins has much of a use-case to begin with. Margins can
still be applied by class on an element by element basis using
“.margined”.
Merge pull request #198 from washingtonstateuniversity/margin-right-namespace

Eliminate cascading margins on column