Get Selenium tests working

[gaurav]

These are in PR #343 and are almost working, except for two things:

• The code isn't correctly waiting for the AJAX requests to the backend to complete before testing the result of the evaluation.
  • Once this is done, I'll go ahead and merge PR Add Selenium tests to Klados #343.
• The goal here is to have a combined Selenium + Jest test, such that:
  • The Selenium test constructs a novel Phyx file and saves it somewhere.
  • The Selenium test runs reasoning on the novel Phyx file or one of the example files, then exports the Nexus representation of the file.
  • We then test the generated Phyx file and Nexus files to make sure they were generated correctly (or, at least, predictably).