Added insert function to the ObjectManager that takes an Object.
Moved the GENERATE_VOLUME_BOUNDS macro to the header file.
New function to find quads of a volume.
Added a separate class for an id generator.

It is also being used in the ObjectManager now.
Added a vector cast to convert vectors of different types.

It can handle an optional converting functions but otherwise uses an
implicit constructor cast.
Added the basis of a tree structure, soon to be a quadtree.