Additional widget e2e tests

- Modified mock-data `additionalParams.html` value to be more realistic and also contain a div with class `.test` to retrieve in a test
- Added comment to settings scenarios "save settings" test to explain why value of `testInput` must be simple
- Added widget e2e tests
- Added a workaround for character encoding requirement for Ace Editor in settings HTML by declaring an import of the generated `settings.min.js` with attribute `charset="UTF-8"` added prior to the build generated script tag that will be produced