Item category references differ from folder names

[plu2k]

Item categories references are in singular and use and as conjunction, whereas folder names are held in plural als use or as conjunction, e. g. "BandagesAndRemedies" vs "BandageOrRemedy".

This is somewhat inconvenient because the ItemsIdMap (for compatibility) uses folder names, and one needs a lookup table to map the new item reference from e. g.
- [ITEMTPL_143, BandagesAndRemedies, 5]
to the category BandageOrRemedy to create a valid item reference. Such a mapping is nowhere in the code and has to be created manually.

Proposal: Change folder names to item category names.