Edupi resource URL should be an URL

[rgaudin]

Almost never used the Edupi resource URI (which should be a ZIP file) apparently accepts any string (A user entered “wikipedia”) which would fail at the installer's download stage.

We should probably check that:

• It's an URI
• It's reachable at the time of addition (HEAD request)

[Popolechien]

Is this still a valid issue since we got rid of Edupi?

[rgaudin]

It's not valid, not because we got rid of edupi (we still allow pre-populated the filemanager) but because it's been implemented