Improve multi-user compatibility (BetterDisplay running in multiple instances under different users)

[taprobane99]

when the new disconnect built-in display when an external display is connected option is ticked, and then I switch to a different user also with that option ticked, the built in display continually switches on and off forever.

[waydabber]

Yeah, the two BetterDisplay processes probably start fighting who gets control. It is advised to disable connection management in case of the secondary user if possible. But will look into it how this could be solved.

[waydabber]

Some forms of brightness control interfere when the app is running in multiple instances under different users.

[waydabber]

The issue here is mostly with colortable manipulation and virtual screens but there are other issues. Any alterations should be disabled if the user that is running the app instance does not have the console.

The official way to check for this is to check kCGSessionOnConsoleKey in CGSessionCopyCurrentDictionary() (https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPMultipleUsers/Concepts/FastUserSwitching.html) - however it is probably not the best idea to do this on every slight change due to the overhead.

An other option (I am leaning towards this) is to simply prevent the app from running in multiple instances by adding LSMultipleInstancesProhibited to the app's properties.

[waydabber]

What I'll do is to put a kCGSessionOnConsoleKey check for events but also cache value so I won't recheck every time but only every 5 seconds or so if needed.