[C2] Delete unused documents when course deleted

[NicoDucou]

In Chamilo 2 when deleting a course it deletes all the registries in the database.
But the files in var/upload/resource are still present.
It is good because resource could be used in many different courses.
So when deleting a course we should check if the resource_file that was used in a course do not have anymore resource_link associated to it then the resource_file registry should be deleted and the file on the disc as well to avoid living unused resources and files.

[ywarnier]

When deleting a course:

• add an option/popup to ask "When deleting this course, the documents available only in this course (if any) will remain available on the platform through the 'File information' tool, available only to the platform administrator. Would you like to delete those documents definitively instead?"
• add an option to the "File information" page to attach an orphan document (one that has no resource_link) to a course (in this case it goes to the root of the documents tool of the course, in hidden mode)
• add an option to the "File information" page to delete an orphan document definitively.

[christianbeeznest]

It is checked and improved with this PR #7068

Thanks for confirmation.

[NicoDucou]

Hi @christianbeeznest
It works but it would be better to have a course selector instead of writing a course code to avoid typing error and people that do not know the code of the course they want to use.

Also as discussed yesterday it would be good to be able to attach a file to a course even if it is not orphan, So we could have a document used in many different courses and on the File Information window we would have on the "Course" line a list of courses and a + at the end to add a course where this document is available.

I accepted the PR because it works how it is now, so you can just complete with those 2 indications.