Expose the minor edit and version summary settings in the administration

minoredit, editcomment and editcomment_mandatory are frequently used in practice, but almost unknown to non-developers. They should be exposed by default in the administration, in a new category regarding edit mode settings, together with the already-displayed settings for default editor, default syntax and mandatory title.

editcomment_suggested and editcomment_hidden are a bit too advanced, hard to explain and break the accessibility by requiring JS to be enabled to work properly, so they are not enabled for now.