Time sig property editor: allows more chars to be entered in the user-defined texts

Time sig property editor: allows more chars to be entered in the user-defined texts for numerator and denominator.

Allows for 'C', '¢', 'O' and 'Ø' to be entered in the text lines for numerator and denominator in addition to digits and parentheses.

This make possible and easy to enter Renaissance or early Baroque time signatures like 'C3' or 'Ø3'.

The usefulness of course is limited to a few niche users, but should not harm the other in any way. The full repertoire of Renaissance and Baroque time sigs is still not covered, as it includes time sigs like "C3/2" or "O6/4"; these will be possible with the (future) more extended time sig editor mainly aimed at (modern) composite time sigs.