generic block element

http://redmine.oerpub.org/issues/495

the objective here was to have a default "semantic block" that is activated on things even if we don't necessarily recognize the specific type of the block. right now the selector is all divs that are not ephemera, not editable and not blocks. i also tore through the existing semantic block ui elements and refactored them to use ephemera so they'd be easier to find.

i didn't test this amazingly because i couldn't find a way to get something unrecognizable into the document to begin with. i did tweak the selector to pick up `p.para` just for giggles and it seemed to work fine.