DNN-4663 Sub-sub-menu items not accessible by mouse

In the DDRmenu, this line makes the sub-sub-menu items too far from the
sub-menu items in such a way that it is impossible to access it without
loosing focus on the parent, so the sub-sub-item disappears before
reaching it.
Merge pull request #52 from valadas/development

DNN-4663 Sub-sub-menu items not accessible by mouse