Feat/better dark mode

[nicolasbraun]

What it si about

This PR is about trying to fix the dark modes issues reported mostly on Mac OS in issues #543 , #707 , #801.

How?

• Add options to customise the header text colors
• Adapt default based on the current system Dark mode status

Limitations

• Does not handle mode switch during execution which can cause some text colors to automatically change (mostly the one not specifically set up and using WX defaults) while the background does not.

Note

Dis not really not again which branch to PR since the 1.0.8 seems to be the current stable release. It should probably be merged as an hotfix. Otherwise I'll try to fix conflicts with 1.21

[k-gruenberg]

This one should definitely be merged! It's such a nice tool/idea but pretty useless if you can't see anything with with light text on a light background (and there being no way to alter the font color)...