Add an option to let the user choose the qt style used by the app

[ctrlaltca]

Fix #2662

[DarthGandalf]

So the -style command line flag will be ignored?

Any way to only change the default, but still honor the explicit user's config?

[ctrlaltca]

So the -style command line flag will be ignored?

Unfortunately yes.

Any way to only change the default, but still honor the explicit user's config?

Should we add an option? This way we could also remove the hardcoded style for gtk3 (#2117).
Hopefully we can get the style from options before the mainwindow get shown to avoid a sudden style change

[AbraxasDMG]

Is the command line switch the only way to apply different style at the moment (no possibility to do it through some config file or environment var)?

If so, KVIrc should also be able to recognize -style cmdline argument and avoid treating it as a server name to which it should connect automatically.

Just realized that this can be prevented if the style argument is provided as follows.
-style=Fusion

Then a new standalone server is not added to the list and automatically attempted to connect to.

[ctrlaltca]

@DarthGandalf please have a look at the second iteration of this patch, I've changed approach adding a new option in theme->general

@AbraxasDMG once we get this working you won't need to provide the commandline parameter anymore

[DarthGandalf]

Haven't tested, but seems fine, I guess