improve graph building, save graph after building it and split of drawgraph

src/c3nav/routing/graph/connection.py

@@ -1,6 +1,8 @@
 class GraphConnection():
     def __init__(self, graph, from_point, to_point):
         self.graph = graph
+        self.from_point = from_point
+        self.to_point = to_point
 
         if to_point in from_point.connections:
             self.graph.connections.remove(from_point.connections[to_point])