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

@@ -6,7 +6,6 @@ from b_asic import \
     Constant, Addition, Subtraction, Multiplication, ConstantMultiplication, Division, \
     SquareRoot, ComplexConjugate, Max, Min, Absolute, Butterfly
 
-
 class TestConstant:
     def test_constant_positive(self):
         test_operation = Constant(3)