Added a few NPE checks to Map.fullInit
All reads on WorldTree.children in WorldTreeFactory now happen
by calling children()
Added method Helper.Hierarchy.HierarchyClass()
Updated parser and all containers to use Helper.Hierarchy
while specifying 'level'
    - This has cleaned up a lot of code
    - Updated Hierarchy.parentLevel and Hierarchy.childLevel
        - No longer static
        - No longer accept parameters

Updated following classes to reflect above changes
    - WorldTree
    - WorldTreeFactory
    - ResolutionEngine
WorldTree no longer constructs itself with constraints from root
Working on pushDownConstraints