Resolve "Operation Replacement in a SFG"

Added method with tests for replacing multiple operations in a sfg with another operation with the same amount of input / output ports. Closes #17

test/test_core_operations.py

@@ -162,4 +162,4 @@ class TestButterfly:
     def test_buttefly_complex(self):
         test_operation = Butterfly()
         assert test_operation.evaluate_output(0, [2+1j, 3-2j]) == 5-1j
-        assert test_operation.evaluate_output(1, [2+1j, 3-2j]) == -1+3j
\ No newline at end of file
+        assert test_operation.evaluate_output(1, [2+1j, 3-2j]) == -1+3j