#602 Add FlatLaf And Themes

[JohnnyBoy]

Its been a while since a new LaF has been added.
FlatLaf is a modern, maintained look and feel.
https://github.com/JFormDesigner/FlatLaf

It has a light and dark theme built in but it also has the ability to add a lot of extra themes (a bit like substance or SkinLAF)
https://www.formdev.com/flatlaf/themes/

The builtin themes work from the extralafs.properties with no extra changes so you probably just need to ship the jar

classname0=com.formdev.flatlaf.FlatIntelliJLaf
jar0=flatlaf-1.1.2.jar
classname1=com.formdev.flatlaf.FlatDarculaLaf
jar1=flatlaf-1.1.2.jar

I imagine the IntelliJ Platform Themes using the .theme.json will require a bit more effort though.

[Gerd Wagner]

Flatlaf was already integrated some time ago. See menu File --> "Global Preferences" --> tab L&F.

I just committed the upgrade from version 1.0 to 1.1.2.

[JohnnyBoy]

Sorry about that.
I was still on 4.1 and didn't notice.