Add a reset button that will only show up if the user edits the JSON configuration for grids. This is a temporary measure until we have a real grid editor GUI in V7. Fixes https://gitlab.com/kicad/code/kicad/-/issues/7595
Fixes https://gitlab.com/kicad/code/kicad/issues/4715
This also gives support for fast grid switching and a user grid to eeschema. Fixes https://gitlab.com/kicad/code/kicad/issues/2200