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 like it but my opion does not really matter for this project. 
This extension is very useful for plugins like WorldGuard or plugins that rely on WG.