Add client application

This client application is imported from https://github.com/jashkenas/backbone/tree/master/examples/todos
Merge pull request #12 from junsumida/add-todo-client

クライアントアプリケーション追加
integrated todo methods
Merge branch 'master' of github.com:junsumida/mosscow
Merge branch 'master' into use-sinatra