Fixed save/load, sfg creating, simulation, bug fixes

Fixed a lot of bug fixes, also added shortcut for creating signal "Space"

b_asic/GUI/main_window.py

@@ -261,6 +261,9 @@ class MainWindow(QMainWindow):
 
         def check_equality(signal, signal_2):
             # check operation types
+            if not (signal.source is not None or signal_2.source is not None):
+                return False
+
             if not (signal.source.operation.type_name() == signal_2.source.operation.type_name() \
                 and signal.destination.operation.type_name() == signal_2.destination.operation.type_name()):
                 return False