[frontend/tasks] Accessibility of tasks groups

[nrybowski]

Is your feature request related to a problem? Please describe.
Practical session exercices are usually gathered in different sections and each exercise has the same accessibility configuration for a same section.
Changing this setting manually for each tasks is a quite inefficient process that should be managed directly by INGInious.

Describe the solution you'd like
Add accessibility restrictions to sections, so that they are applied to each task of the section at once.

Additional context
This feature should be envisonable with the new course definition.

[Drumor]

Same as #914 no?

[nrybowski]

#914 was more about hiding a whole section when the 'Closed by default' radio is selected. This feature request is related but asks for more control on the way a section is hidden or not.

If this issue is truly duplicate, we can add this feature request in #914.

[Drumor]

Nevermind, miss understood the initial request. @anthonygego says it's in his todo list.