Give option to allow results without a main image

[aendra-rininsland]

Presently all results have to have a main image due to this filter.

It would be rather trivial to make this configurable, and would be desirable in some circumstances (e.g., when returning a list of related links for things like the card-y stream-y pages like Trump's Cabinet).

Marking as "bug" because it really should be fixed and ultimately prevents Onward Journey from working as expected (the requirement for images isn't documented anywhere).