Add nofullscreen to windowrules

[DashieTM]

Describe your PR, what does it fix/add?

Provides the ability to disable fullscreen mode for applications.
Most used for applications that request this for no reason.
-> potentially fixes #1074

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

I Have tested this in debug mode and with a few applications, more testing is always welcome.

Is it ready for merging, or does it need work?

A quick check whether or not I have left out some edge cases and if the rule is done properly, just applied the way the other rules were applied.

[vaxerski]

I think it would be way more useful if this only disabled the app requesting fullscreen, and not fullscreen altogether. If the user uses a keybind to toggle fullscreen, why should we not allow them to do so?

[DashieTM]

Sure, we can also do that instead.
Are all the calls to setWindowFullscreen from the requests in windows.cpp?

[vaxerski]

Are all the calls to setWindowFullscreen from the requests in windows.cpp?

Ye

[vaxerski]

Make a wiki MR and I'll merge this. Thanks!