Extent Enhancement

This pull request is to make Extent into an object intended to redefine origin relative to a parent Extent up until a root World and make locations represent the local coordinates of the extent it contains.

This would be useful for any region based system, allowing them to reference local coordinates. An example would be an arena object implementing extent, possibly with sub regions for the arena parenting off of the arena. Creating a copy of this arena layout would be as simple as changing the origin of the new copy.

Personally I don't expect this to get merged as I know there are some issues with my way of handling it, however I did this to bring attention to the possibility of what can be done with Extent. This is just something I did to show how it could be done.
I figured it wasn't a good idea to cause the creation of many Vector3d instances from within a loop, especially when the addition is so simple to do like this.