Admin: Js validation: missing tests for invalidated saving of form with multiple options (checkboxes)

[boris-brtan]

What is happening

We don't know whether there are some problems with checkboxes during filtering or saving forms. When there is some exception and validation fails and form is submitted which is not the right scenario.

Expected result

We have selenium tests for saving of invalid form with checkboxes. So we will know that there is some error if form is submitted.

[boris-brtan]

will be solved by #260