Allow adding new layers (displayable items) to avatar

[igorko]

Mainly this makes equipment slots order not important for avatar drawing. Also allows you to add new item types (layers) that can be equipped. E.g. we can add hands/legs item types and draw them separately. Layers order definitions moved to config file, though definition system will be changed. Required layers for this implementation to work are "body" and "head" types(as it was before). Now you can remove the rest without touching source code ;)

Bonus: fixed MSVC build.

[clintbellanger]

Pulling this. We may simplify/iterate later.