Isolate tests from application structure

[aaron-schroeder]

This makes it easier to not include the tests when deploying the app on docker etc.

• [x] Move tests dir from application/ to top level.
• [x] Ensure tests are passing by modifying the test files only
• [x] Add tests/ to .dockerignore
• [x] See if this makes for a faster docker image creation process as well as a smaller image.
  • Not noticeably faster (pip installs are the main thing)
  • Same size image. Probably, those dependencies make up the bulk.
• [x] Update README to reflect modified unittest commands