Open guest showcase

[torss]

User Story

As a:

1. guest
2. teacher / administrator

I want:

1. to see information about available courses without having to (be able to) register
2. to strictly control which information is openly available

so that:

1. I can properly evaluate whether or not the courses are interesting.
2. no course-internal (e.g. copyrighted) information is leaked.

Acceptance criteria:

• [ ] A course can be set to "guest-visible" by a teacher, which allows publication of the general course information (i.e. name & description) in the showcase (see below).
• [ ] Units of a course can be marked "guest-visible" by a teacher, which makes them visible but not editable by guests, iff the course itself is also marked "guest-visible".
• [ ] A warning about the consqeuences of marking something as "guest-visible" is given and must be confirmed, to avoid accidental publications.
• [ ] All "guest-visible" courses (and "guest-visible" units within) are accessible without login via a course showcase on the landing page.
• [ ] "guest-visible" also implies showcase and "Available Courses" visibilty for courses with non-"free" access type.

Additional info:

Perhaps a better term than "guest-visible" should be used. It could perhaps simply be called "open" or "public", but that might be confusing with respect to the course access type "free". Setting an entire course (i.e. including all units) as "guest-visible" may also be useful, but is not yet considered important in this issue.