Also simplifies the dialog by removing the user grid (now that you
can add as many user grids as you want).
This does mean that you can no longer have an asymmetric grid, but
it gets too complex if we allow everything for everyone.
For the sake of consistency across all dialogs and window that behave
like dialogs, remove the static line that separates the main part of
the dialog from the standard buttons. This only applies to windows
that have the standard button on the bottom of the frame.
This covers the 3D viewer, CvPcb, common, GerbView and KiCad dialogs.
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