make semantic draggables look more like mock-up

The changes here in github-bookeditor include separating the semantics
bar from the other icon toolbar and some more variable usage mostly so
that things line up. Forthcoming change in Aloha-Editor.
undo absolute positioning

the padding + negative margin is to make the scrollbar extend up to the
beginning of the gray area ... as opposed to just starting where the
semantics end.
make semantic bar higher than "copy [element]"
Merge pull request #104 from oerpub/style-semantics-like-mockups-58860600

make semantic draggables look more like mock-up