Refactor

[SakibulMowla]

• [ ] Refactor matcher.test.js
  • [ ] Create user const and move test users there
  • [ ] Add more test
  • [x] refactor the big test
• [x] Move tier arg to class constructor
• [x] Create common const library
  • [x] Move db timeout constants there
  • [x] Move db name constants there
• [x] Refactor Matcher
  • [x] decompose getPreferenceList
• [x] Move files under src, test directories