Merge branch 'newer-networkx' into 'master'

Adapt to newer networkx, which refuses hold=True argument.

See merge request !16

plotting.py

@@ -208,7 +208,7 @@ class PlotUI:
                                 node_size=PlotUI.nodesizes[type],
                                 node_color=nodecolors,
                                 alpha = nodealpha,
-                                hold=True)
+                                )
 
 
          self.plottednodes[nodec] = nodes
@@ -269,7 +269,7 @@ class PlotUI:
                                 style=PlotUI.edgestyles[type],
                                 alpha=ealpha,
                                 arrows=False,
-                                hold=True)
+                                )
          else:
             self.edgec = nx.draw_networkx_edges(graph, pos=data['pos'],
                                 edgelist=edges,
@@ -278,7 +278,7 @@ class PlotUI:
                                 style=PlotUI.edgestyles[type],
                                 alpha=ealpha,
                                 arrows=False,
-                                hold=True)
+                                )
 
       if 'labels' in data:
          color = 'k'
@@ -292,7 +292,7 @@ class PlotUI:
                                  font_size=fsize,
                                  font_color=color,
                                  alpha=1,
-                                 hold=True)
+                                 )
 
       if 'edgelabels' in data and not edge_cmap:
          self.elabelc = self._plot_edge_labels(graph,