[core] graph: Trigger onGraphUpdated slot when chunks change

`onGraphUpdated` updates the models for chunks, including the placeholder,
which allows to have an up-to-date status for all the existing chunks as
well as the placeholder one when a node's number of chunks hasn't been
determined yet.

Author: cbentejac

meshroom/core/graph.py

@@ -500,6 +500,7 @@ def _addNode(self, node, uniqueName):
         node._name = uniqueName
         node.graph = self
         self._nodes.add(node)
+        node.chunksChanged.connect(self.updated)
 
     def addNode(self, node, uniqueName=None):
         """