ClassName changes and method addition

-ClassName 'ActiveDepartment' and 'ActiveEmployee' now become 'Department'
and 'Employee'
-added method 'isActive' and 'findByStatus' in 'Employee' Class
fix some bugs in class 'Paginator'
add null return value if data not found in Ms. SQL Server query
fix wrong number of rows generated by PDO 'SELECT' query