MainWindow: Add minimal info tab.

src/Model/Network/Graph.py

@@ -67,6 +67,13 @@ class Graph(object):
     def edges_counts(self):
         return len(self._edges)
 
+    def enable_nodes_counts(self):
+        return reduce(
+            lambda acc, n: acc + 1 if self.is_enable_node(n) else acc,
+            self._nodes,
+            0
+        )
+
     def enable_edges_counts(self):
         return reduce(
             lambda acc, e: acc + 1 if e.is_enable() else acc,