Force thesis projects to be assigned to at least one course edition

It seems possible to create thesis projects which are not assigned to any courses, which makes them inaccessible. It should be enforced for a thesis project to be added to a course edition, perhaps the default should also be to add a thesis project to all (selectable) course editions.

Additionally, the edit page in the management panel should have a popover to explain why users need to specify course edition.

Other things to think about: perhaps we want a blacklist rather than a whitelist for this, as new programmes would likely want to have the thesis projects displayed unless indicated otherwise.