Add new note-input command to create grace note chords in tablature

2.0.3 / Win 7/10

Issue

There is currently no way to create a grace note chord directly in tablature, such as the following:

Possible solution

1. Will apply only to tablature and allows grace note chords to be created in the same voice.
2. The user would select an existing acciaccatura (say) in non-note-input mode (say), and press [Alt] + [string number].
3. This would create another note in the same chord on the desired string (= "string number"). The fret number will be the same as the originally-selected note.
4. The user can then use the up/down arrows to edit the note.