[frontend/administrator panel] Ease of access to the accessibility parameter

**Is your feature request related to a problem? Please describe.**

When a course contains tens of exercises, it becomes hard to determine from the administrator panel which ones are actually accessible to students and which ones are not.
It requires entering edit mode for each task one by one in order to know which value the accessibility setting is being set to.

**Describe the solution you'd like**

Adding an indicator that visually provides the accessibility information or even better, a button/checkbox to switch from one to the other in 1 click.
This could be a 5th button displayed on the right side or preceding the task name in case of a checkbox: