Added capability to edit and delete edges.  Edited nodes/edges are now postfixed with '*' to denote an edit.  Merged nodes now have a black border around them to differentiate them from any other node types.
Shift + Ctrl on node click will select all nodes of that type.  Shift + Alt on node click will select all neighbors of that node.  Shift on node click will not deselect any previous selections.  Normal click will deselect everything before selecting clicked node.