Options panel use GTK default colors

[hectorespert]

Use default colors in options panel when GTK laf is used.

Tested in Ubuntu 20.04 with default theme.

Before:

After:

[neilcsmith-net]

Sorry, -1 from me on this. Although +1 to fixing it. We can't keep adding exceptions for look and feels over the code base. Better to fix this so that a single key works for all LAFs. If separator.foreground doesn't work for all, maybe a specific key for this panel that does?

[hectorespert]

Sorry, -1 from me on this. Although +1 to fixing it. We can't keep adding exceptions for look and feels over the code base. Better to fix this so that a single key works for all LAFs. If separator.foreground doesn't work for all, maybe a specific key for this panel that does?

I added a keys to modify this panel to allow remove LAFs exceptions but this PR only removes exceptions for the GTK laf.
I can't test other LAFs and they could be modified later.

[lkishalmi]

A step in the good direction, though if we are adding new LAF keys, probably shall add constants for it in LFCustoms.
And by introducing that it would be good to check if all supported LAF-s are providing defaults for the new key.

A sidenote: It would be really great if you could detect somehow when the GTK skin is set to dark, if it does, it would be great at least add the "nb.dark.theme" to true.

[hectorespert]

A step in the good direction, though if we are adding new LAF keys, probably shall add constants for it in LFCustoms.

I added the new constants in LFCustoms.

And by introducing that it would be good to check if all supported LAF-s are providing defaults for the new key.

New keys are only used by GTK theme, I would like to fix the problem with that theme before start to modify the other themes.

A sidenote: It would be really great if you could detect somehow when the GTK skin is set to dark, if it does, it would be great at least add the "nb.dark.theme" to true.

A GTK configuration property to detect that is available: https://developer.gnome.org/gtk3/3.8/GtkSettings.html#GtkSettings--gtk-application-prefer-dark-theme

[geertjanw]

Changing milestone to 12.5.

[ebarboni]

@neilcsmith-net @lkishalmi are the changes better now ? Can we consider merging ?

[lkishalmi]

Generally I'm Ok with the implementation, just those constants...

[ebarboni]

change resquested moving to 12.6 for now

[neilcsmith-net]

@lkishalmi please review and merge if you're happy.

[matthiasblaesing]

This seems to be a working implementation, which even looks like a cleanup. Any reason not to merge now? (the unittests that fail are known to be flaky).

[hectorespert]

Any reason not to merge now?

It's only waiting for a positive review.

[lkishalmi]

Seems to be fine now.