Use std::unordered_map instead of std::map

[Rubonnek]

I inspected the code again and I think it's better to use std::unordered_map for bodyDefs and bodiesInFile instead since std::unordered_map is a faster container for accessing individual elements.

The only time the code loops over bodyDefs is for removing all the shapes, which is where we are shifting the performance hit to since the std::unordered_map container is slower in that case.

I'd rather have faster object creation by using std::unordered_map than faster object removal by using std::map.