BUG: Fix bug causing missed shared vertices in topology converter.
Checking for shared faces is not enough when inserting vertices to generate higher order elements. Matching faces depends on the order of traversal of the elements. Now we check for shared edges in addition to faces - this solves the traversal ordering problem as we will pick up cases where two elements share an edge before the faces can be matched. Before, this caused duplicate points to be inserted on the shared edge.