Description: 
In <number:fraction> element, Gnumeric treats both attributes min-denominator-digits and max-denominator-digits (see bug 38097#c27), while LibO knows only min-denominator-digits like ODF 1.2 standard:
http://docs.oasis-open.org/office/v1.2/cs01/OpenDocument-v1.2-cs01-part1.html#element-number_fraction

ODF 1.3 will include max-denominator-digits:
https://issues.oasis-open.org/browse/OFFICE-3695

LibO should now also treats this attribute. As actual LibO treats "min-denominator-digits" as the maximum of denominator digits, backward compatibility should carefully checked.

IMHO, when importing:
- if both attributes (min and max-denominator-digits) are present, treat them normally (it would be great also to import gnm:max-denominator-digits as number:max-denominator-digits)
- if only min-denominator-digits is present, consider it as max-denominator-digits and set min-denominator-digits to 0
- format string should be build with n_q number of '?' and n_z number of '0', with n_z = min-denominator-digits and n_q = max-denominator-digits - min-denominator-digits

Main issue will be when exporting. As min-denominator-digits="0" is not recognized (see bug 38097#c27) with actual version of LibO, fraction format will be lost if file is opened with actual or previous version. This should be exported to specifically ODF 1.3