Use GroupedOperation for merging PlatformPhyisicsOperation

PlatformPhysicsOperation.py

@@ -1,27 +1,30 @@
 from UM.Operations.Operation import Operation
 from UM.Operations.AddSceneNodeOperation import AddSceneNodeOperation
 from UM.Operations.TranslateOperation import TranslateOperation
+from UM.Operations.GroupedOperation import GroupedOperation
 
 ##  A specialised operation designed specifically to modify the previous operation.
 class PlatformPhysicsOperation(Operation):
     def __init__(self, node, translation):
         super().__init__()
         self._node = node
-        self._translation = translation
+        self._transform = node.getLocalTransformation()
+        self._position = node.getPosition() + translation
+        self._always_merge = True
 
     def undo(self):
-        pass
+        self._node.setLocalTransformation(self._transform)
 
     def redo(self):
-        pass
+        self._node.setPosition(self._position)
 
     def mergeWith(self, other):
-        if type(other) is AddSceneNodeOperation:
-            other._node.translate(self._translation)
-            return other
-        elif type(other) is TranslateOperation:
-            other._translation += self._translation
-            return other
-        else:
-            return False
+        group = GroupedOperation()
 
+        group.addOperation(self)
+        group.addOperation(other)
+
+        return group
+
+    def __repr__(self):
+        return 'PlatformPhysicsOperation(t = {0})'.format(self._position)