Avatar clothing files

This adds functions for loading the clothing data of an avatar from a file or 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")
```

Loading the clothing from a file with the **local avatar** will have the following special cases:
* If the gender in the clothing file is different (Male vs. Female) the player model will be changed.
* If the file does not exist the avatar will be hidden. (Used in startup)