Added missing interface method to obtain unionType from conditions

Moved constraint resolution to its own package
    This change separates constraint resolution methods and
    logic from the core WorldTree class

    The idea is to allow pluggable constraint solvers

    A constraint solver can be plugged in by changing the currently
    hard-coded intialization in ConstraintSolver class

Working on brute force constraint solver

Removed some warnings from various files
QueryResolutionEngine now uses CONSTRAINT statement case to handle
constraint queries
Finished implementing brute force constraint solver
    - Tested with simple constraints