Workaround for special characters

[atomczak]

Markus Järvenpää raised the issue that Finnish classes, properties and property sets often need 'Äą'. In bSDD we allow 'Äą' in names but not in codes.

Problem 1: The property set doesn't have a name in bSDD, only code. A potential workaround could be to define the set as GroupOfProperties and give it a human-friendly name with 'Äą'. But it's not supported by software implementations and also leads to problem 2.

Problem 2: Common BIM software allows users to put property names with 'Äą', and when exporting to IFC, those characters get encoded to hexadecimal code (https://technical.buildingsmart.org/resources/ifcimplementationguidance/string-encoding/). bSDD doesn't allow '' in codes, so not possible to define even the encoded names.