demo how to share service between directives(MVC design pattern)

• directives -> service
• service hold data model and its status
• directives are stateless
• directives use different direction to view service data
• directives don't know each other
• the whole app didn't use AngularJs watch, emit or broadcast
• service lightly depend on angularJs ,can easily migrate to other UI framework
• most of business logic is in service