RelationUtils.element: fix switched domain/codomain
make editors more compact

- hide top bar with title/icon
- merge domain/codomain button with +/-/done buttons
- remove relation type switching button and make same functionality
  when you click the part of the relation path that you're already in
- fix big codes breaking relation editor domain/codomain buttons
display relations using color coded block graphics

-remove RelationUtils.element for now;
 it's too complicated, buggy, and unspecified.
 use dummy relation (empty union) instead
-document rebase and reroot
-reRoot -> reroot
RelationPath: show colored blocks instead of symbols
remove unused relation layouts