Fix bugs and add new Features

• Removed redundant company constraint on employee table
• Changed primary and secondary key type to unsigned integer
• Add new functionality: Dynamic load states base on country and cities base on state
• Fixed migrate issues

• Instruction

• Clone the new version of code at above branch
• Run migrate command again "PHP artisan migrate"
• Run seed command again "PHP artisan seed"
• Fixed issue: cannot add employee after applying dynamic loading state and city.
• Show error to GUI when user doesn't select department and division
• Dig into the source code of Enhance version