Avatar clothing files

This adds functions for loading the clothing data of an avatar from a file as well as saving it to a file. These functions can be used in python scripts (for player avatars and NPCs as well) and are e.g. required for the new startup age by @ChristopherS and me.

The python functions will use the file in *%UserData%/Avatars* if only a filename is given. Otherwise the given path will be used.
*For example:*
```
# This will save the clothing to [LocalAppData]\Uru Live\Avatars\test.clothing
PtGetLocalAvatar().avatar.saveClothingToFile("test.clothing")

# This will load the clothing from [Client]\dat\clothing.file
PtGetLocalAvatar().avatar.loadClothingFromFile("dat/clothing.file")
```

If the gender in the clothing file is different (Male vs. Female) and we are loading the local avatar, the player model will be changed.

Counterpart is H-uru/moul-scripts#56