marksAndBreaks: Update origLineBreak

orignLineBreak now sets the shortInstrumentName of the next system to "".
This gives a better visual indicator of the fact that there is an additional break
Add roman numerals conversion snippet

This is a conversion routine between integers and roman numerals.
This may be useful for numbering variables with roman numerals.

For now it is a Frescobaldi snippet, but it can easily be changed to a
normal Python function.
I don't know yet how I can make it process a whole document. So probably it will be better to be used inside a regular Python script that writes .ly or .ily files

Next step to be done would be to implement a sorting mechanism