Add functional tests

[redshiftzero]

While we have unit tests, for maintainability it would be useful to additionally have functional tests that verify the behavior of the application from the perspective of the user. There's a pytest-qt plugin which enables one to test in this manner by simulating the user's mouse clicks/keyboard input.

[eloquence]

We discussed today that for the 2/5-2/20 sprint, it would be useful to do an exploratory spike on this -- meaning, evaluating e.g. the pytest-qt plugin to see if we can automate some of the scenarios covered in the client test plan and and the beta acceptance tests.

Potentially a good issue for @ntoll, but any release blockers he can help with should take priority.

[ntoll]

👍