It is possible to filter questions depending on the questionnaire in the Django Admin interface.
It is possible to show all questionniare questions when adding show_all=1 GET parameter.

It is useful for debugging purposes, when you want to see all questions rendered
on one screen.
Increased the max_length of the Question#checks field to 512.

In cases of some custom fields, we need to put a lot of information into this field.
If the OPEN field was saved as empty there was an exception when trying to load its previous value.