Polish types API

• ClassGenerator does not add NonCheckedClassType into use statements. That could be fixed with common interface for ClassType and NonCheckedClassType, but they actually do the same things except for constructor so they should inherit one from the other. As ClassType has more specific behavior (class existence checking), it should be renamed to CheckedClassType and should inherit from NonCheckedClassType which should be further renamed to more general ClassType.
• remove classType() in Types/functions.php – !16 (merged) provides cleaner/more explicit API