[JW Lua] Font constants missing for "Parts" fonts

[Jan Angermüller]

Jari,

in Document Options->Fonts it's possible to assign different fonts to 
Time Signature (Parts)
and Time Signature (Score), and Time Signature Plus (Parts) and Time 
Signature Plus (Score).
It was probably introduced to be able to create huge time signatures in 
scores.
The "Parts" fonts are missing in FONTPREF_CONSTANTS.

Jan