Updating permissions system

Description

Simplify the permissions system by:

• Groupping all the permissions
• Differenciating author and student role

This will improve code readability.

Migration and compatibility

• The merge request DOES NOT update the models. If it does, database migrations are needed after merging, add the label Database migrations
• The merge request DOES NOT break the compatibility.

TODO

Before being accepted, any merge request must fulfill the following requirements:

• Check PEP8 writing style as described in CONTRIBUTING.md.
• Ensure existing tests are still working properly.
• Features have been tested.
• Every translatable strings are written in proper english.
• Every translatable strings are tagged for translation using gettext, blocktrans and/or trans.
• Ensure that there is no side effect in files: changes are only related to one, and only one feature.
• Ensure that no file has been removed by accident.
• API is documented, as well as the behavior, if needed, in docs.
• Ensure the commit history is “clean enough” (this means no extra merge commits, etc).
• Ensure pipeline succeeds.

git checkout <feature_branch>  # Switch to the feature branch
git fetch --all --prune  # Download new commits
git reset --hard <remote>/<feature_branch>  # Override your local worktree with the one from remote branch

Impacted Areas in Application

This impacts huge parts of the code because the permissions system is used every where (in view, models). But with no huge code modification.