CLIMATE-416 - Simplify UI backend test file download

- Add package wide test setup.
- Move all example file downloads into the package wide setup. Files are
  only downloaded if they're not currently on the system. This keeps
  stuff from being downloaded every time tests are run.
CLIMATE-416 - Remove test assert from test_processing
CLIMATE-416 - Fix test working directory issues

- Move working directory creation to package wide setup.
- Remove all working directory clean up calls from tests. The working
  directory used in the tests overlaps with the one used by the toolkit
  during actual evaluations. We can't remove the working directory if
  there are actual run results present, so instead cleanup is performed
  only on the additional artifacts that we create in the working
  directory.
- Fix bad directory tests. Many of the result listings were testing an
  older format that was no longer valid.
- Add a helper for cleaning the results listing responses to exclude any
  possible run folders from actual toolkit evaluations. Other tests that
  exercise the toolkit are also writing test results to this directory.
  Now any folders that are appropriated named are removed before the
  results listing is tested.
- Move WORK_DIR definition out of specific classes an into the module in
  test_directory_helpers.
CLIMATE-416 - Remove Unary metric load from processing test

- At the moment, all Unary metrics are excluded from the UI. The metric
  load test was attempting to load a unary metric which was causing it
  to fail. The test is now done with only binary metric(s).
CLIMATE-416 - Remove web services init test

- The initialization test in run_webservices was not especially useful.
  It would simply check if it got a 200 back from requesting the UI's
  index. Additionally, if the frontend was not symlinked in the location
  that the backend expected the test would break. In light of this, the
  test has been removed. The other tests which setup a faux backend are
  sufficient to ensure that initialization is correct while also not
  being as brittle.
CLIMATE-417 - Add ASF headers to backend test files.
Resolve CLIMATE-416. Merge PR #24.
Resolve CLIMATE-417. Merge PR #25