Diatonic Accordion Tabulature for "Griffschrift"

I want to implement a Tabulature for Diatonic Accordion in "Griffschrift".
Additionally semi-automated translation from standard staff shall be supported.

There is a feature request "Tablature for accordion" by vgStef
(http://musescore.org/en/node/24695#comment-95577),
As the request by vgStef deals with an other kind of tabulatur I opened a new request.

The "Griffschrift" tabulature has 5 lines and uses the standard
note symbols to encode the length of the note.
Each note symbol corresponds to a button on the accordeon.
A more detailed description of "Griffschrift" notation can be found in the following link:
http://www.volksmusikschule.at/enggriffschrift1.htm
An example of a complete score can be seeh here:
http://www.stammtischmusik.at/noten/antanzfuernfranzgs.htm

For the implementation of "Griffschrift" support the following features need to be coded:

- for writing the notes:
=============
the following symbols are required
o "normal" note - for first and second button row
o note with double sharp (or any similar symbol) - for third and fourth button row
o letter below the system - chord for left hand
o a fat horizontal line below the letter, which is linked to the note
- this indicates "push" during playing that tone and influences the pitch

- for playback:
=========
I am thinking of some kind of reference table, which assignes each position
in the staff a freely defined pitch, depending on the presence or absence
of the horizontal line and the double sharp.

- for semi-automatic translation:
===================
Translation from standard to tab notation shall be supported. The difficulty with
diatonic accoreon is that some notes can be played on different buttons.
Thus the translation process must be interactive.
The translation procedure could work like this:
o create a system with one standard and one tab staff
o enter the notes in the standard staff
o when you execute "translate" an initial version will be written into
the tab staff.
o when you change to a "fine tuning" mode all notes, which can be played
by alternative buttons are marked in a different color, when those notes are
selected in the tab staff, all alternatives can be checked.

I would like to implement these features by myself, but when I looked throught the code
I noticed that I will need some help on where to attach those features and how to fit
the requirements into the data structure.

I will be happy to read your feedback.