Implement QuadTreeAware interface and allow "upwards" searching of QuadTrees

[tomcashman]

Currently we can only search down a quad tree but since a lot of searches are relative to an element in the tree, we can optimise searching by searching upwards from a quad. Add a 'QuadTreeAware' interface that elements can implement that allows for set/get of quads. Then add versions of the contains methods that searches upwards instead of down.