[IMP] website_slides: add possibility to request access to private course

PURPOSE

Before this commit, a user could not contact a course responsible to ask him
to join. With this commit he is be able to do it.

SPECIFICATIONS

Change the message 'Contact website administrator' to 'Contact Responsible'.

Add the name of the course responsible in the course description panel. When
clicking on its name it opens a modal to request access to the course. It
creates an activity linked to the customer and assigned to the responsible.

When hovering the 'You're enrolled' button the fa-check icon changes to a
fa-times icon to show that you can unsubscribe when clicking.

LINKS

Task ID : 2127364
PR : #40708