Fix webui unit-tests

I've tried to run webui unit-tests. Here's what I did:

rake build_ui
export CHROME_BIN=chromium
cd webui
npx ng test

An example error in the first comment.

We should:

1. investigate why the tests are failing. If they're non-sense, mark them as such.
2. extend developer's guide with a description how to run webui tests. A single section or a list of steps will do.
3. look at running those tests as part of CI.

The last step can easily be moved to a separate ticket.