Staff type dlg box: Relevant staff templates only

In staff type dlg box, only displays staff templates from groups relevant for the staff instrument.

Also:
- removes the default guitar string data, which does not make sense for non-stringed instruments (stringed instruments are assumed to have proper string data in instruments.xml anyway); default string data now has an empty string list, which is used as a mark that the instrument does not support tablature.

- Renames `stafftype.ui` to `editstafftype.ui`.
- Cosmetic fixes to `editstafftype.ui`: tab order and buddies