Move src to cura so we can use the same package for installed and source

Contributes to #41
Contributes to #42

cura/PlatformPhysicsOperation.py

@@ -0,0 +1,33 @@
+# Copyright (c) 2015 Ultimaker B.V.
+# Cura is released under the terms of the AGPLv3 or higher.
+
+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._old_position = node.getPosition()
+        self._new_position = node.getPosition() + translation
+        self._always_merge = True
+
+    def undo(self):
+        self._node.setPosition(self._old_position)
+
+    def redo(self):
+        self._node.setPosition(self._new_position)
+
+    def mergeWith(self, other):
+        group = GroupedOperation()
+
+        group.addOperation(self)
+        group.addOperation(other)
+
+        return group
+
+    def __repr__(self):
+        return "PlatformPhysicsOperation(t = {0})".format(self._position)