Obey multi-digits fret nos. in staves linked to a TAB staff

If another staff is linked to a TAB staff, entering the 2nd (or more) digit of a multi-digit fret number has no effect in the linked staff.

Fixed by iterating the fret no. change on all the notes linked to the note being edited.

Issue has been reported in the MuseScore French forum: http://musescore.org/fr/node/21296#comment-85785 but it has not a issue report yet.

Note: is it reliable to assume that elements linked to a Note are also Note's?