Re-grouping and ordering the editing preferences

Re-grouping and ordering the editing preferences

Arange the settings in three groups: How to call the editor, how
the editor looks and how the preview works. The only toolbar
preference is at the bottom because the WikiEditor extension adds
its stuff there. All the preferences are untouched. This does not
add or remove a preference.

Goes with Id8b9a47a in the WikiEditor extension.

Change-Id: I429c8125b8db789d2756d61249f6cf1fa7f2f51c