Added automatic Swagger testing for GET endpoints

- Added swaggerTestHelper.js to automatically test GET endpoints.
- Changed swagger.yaml version field to string (there's a problem with swagger-parser and its dependency swagger-schema-official.
- Refactored most defined request data objects to sampledata.js.
- Added a test to the Challenges API to test all GET endpoints related to challenges.
We actually don't want these fields on the FileResource or the file table.  This is an issue we need to fix in a follow up challenge.  It's ok to have a test failing.  See related issue: https://github.com/appirio-tech/lc1-project/issues/187