Network: Add delete node undo command.

src/Model/Network/Graph.py

@@ -101,7 +101,7 @@ class Graph(object):
         return self._add_node(node)
 
     def insert_node(self, node):
-        self._add_node(node)
+        return self._add_node(node)
 
     def create_node(self, x:float = 0.0, y:float = 0.0):
         node = self._create_node(x, y)
@@ -126,6 +126,9 @@ class Graph(object):
                                status = self._status)
         return self._add_edge(edge)
 
+    def insert_edge(self, edge):
+        return self._add_edge(edge)
+
     def remove_node(self, node_name:str):
         self._nodes = list(
             filter(