Implement __copy__() and __deepcopy__() for Forces

wrappers/python/src/swig_doxygen/swig_lib/python/extend.i

@@ -201,4 +201,16 @@
         self->getPerDofVariable(index, values);
         return copyVVec3ToList(values);
     }
-}
+}
\ No newline at end of file
+
+%extend OpenMM::Force {
+  %pythoncode {
+    def __copy__(self):
+        copy = self.__class__.__new__(self.__class__)
+        copy.__init__(self)
+        return copy
+
+    def __deepcopy__(self, memo):
+        return self.__copy__()
+  }
+}