Handle the PiDP-11 Data Selector switch press

[thieleke]

@obsolescence - it's great to see you and your code on Github!

Here is a modification I made back in 2019 which uses the Data Selector button push to either run a system-specific script, or if there is no script, simply locks the panel - which is how I typically use it. It is great for preventing accidental reboots if you press the Address Selector button, for example.

From the including support script:

Search for a "data_switch.sh" script in the currently selected system's directory 
(e.g. /opt/pidp11/systems/idled/data_switch.sh) and exit with its return value, if it exists.  

Otherwise toggle the Panel Lock functionality.