Moved CheckExpr visitor to new package based on Tijs' feedback
Renamed Numeric expressions to Arithmetic expressions based on Tijs' feedback
Moved And, Or expr to subpackage logical expressions
Added BinaryLogicalExpr superclass
Refactored And, Or classes to extend new BinaryLogicalExpr superclass
Renamed binary boolean expr package to relational expr package
Renamed BinaryBoolExpr superclass to BinaryRelationalExpr
Refactored CheckExpr visitor to reflect changes in relational and logical expr checking