Add collapsable/deployable groups

[Flatkat]

These would serve as a better way to organize a long tab of configs or help on not bloating too much the config screen when you have multiple minor settings related one specific feature inside a tab.
Would be great if you could set wether it is opened or closed by default and were nestable.

Image from YACL showing its "groups" implementation:

[Motschen]

This is very doable, and could even re-use code from comments and conditions.
I'll implement it in one of the next updates :)