refactored app.js and api.js.
Merge pull request #7 from paulyi326/dev

refactored app.js and api.js.
Add basic mocha/chai testing framework
(test) Integrate supertest; Implement GET unrecognized route
Comment out pending testcases
(test) Implement root GET test
(test) Implement create yarn and get all yarns server tests
(test) Update tests to fit new server API