Resolve "Replacing Operations in SFG"

I added some thoughts on how this issue was implemented in #15 (closed), for most part on how we handle replacing several operations. Closes #15 (closed)

b_asic/core_operations.py

@@ -192,7 +192,7 @@ class ConstantMultiplication(AbstractOperation):
     TODO: More info.
     """
 
-    def __init__(self, value: Number, src0: Optional[SignalSourceProvider] = None, name: Name = ""):
+    def __init__(self, value: Number = 0, src0: Optional[SignalSourceProvider] = None, name: Name = ""):
         super().__init__(input_count = 1, output_count = 1, name = name, input_sources = [src0])
         self.set_param("value", value)