3 row accordion fingering

This plugin will write fingering (button number) for a 3 row accordion below the staff. The annotation is based on Corgeron. i.e. 1 line per row of buttons on the accordion and the button number is underlined when the accordion must be pulled.
If there are several possibilities to play a note, these are all written.
On running the plugin, the user will be prompted to enter:
- the position below the staff to write the button numbers of the first row
- the distance between two rows
- the separator to use (when a note can be played differently on the same row)
If one or more measures are selected when running the plugin, only those measures will be annotated. Otherwise, the whole score will be annotated.