Added tests for IntervalKDTree.
Moving things around.
Moved ikdtree and indexabletable to namespace structure.
Split Box to another file and some code refactoring.
Created SWIG module for ugdk::structure.
Add operator array for Vector2D.
Changing class Item.
Fix IntervalKDTree and Node interfaces.
IntervalKDTree FindIntersectingItems now uses output iterators.
Build fixes.
Merge branch 'ikdtree-refactor' into dev
Fix example 2.