CIF simulator GUI input mode termination by red stop button leaves buttons enabled

In #216 (closed) we ensured that after the red stop button on the Eclipse 'Console' is clicked, this 'immediately' terminates the CIF simulator, even when using the GUI input mode, rather than it being delayed until another choice is made.

One thing I noted is that if you do that, the buttons remain enabled, while the simulation ends and the buttons thus don't have any useful effect anymore. The simulator should probably inform the GUI input component of the termination, such that it can disable the buttons.

Note that clicking the still activate buttons has no effect as the simulation has terminated. Clicking a button then does disable all the buttons until a choice is to be made, which will never happen as the simulator has already terminated.

It can be confusing for users that buttons remain enabled while the simulation has terminated, as clicking the buttons no longer has any effect.