Re-organize code structure

[wuyichen24]

• Move service class from domain to service package (create a new service package).
• Move entity class from domain to models package (create a new models package).
• Move repository class from domain to repository package (create a new repository package).
• Move main class from domain to root package (example: move OrderServiceMain.java from net.chrisrichardson.ftgo.orderservice.main to net.chrisrichardson.ftgo.orderservice)
• Move controller class from web to controllers package (create a new controller package).