Add event images

[mblayman]

It would be cool if we could pull down event images if they are available from the various connectors. We could add an event image to the event detail page. We could also restyle the event card and use a small image for that.

This wasn't really feasible before when we were storing images in the repository. It would have been too much data.

If we do this, we should consider having a nice placeholder image or else the card or detail page might look a bit lacking if the updated design expects an image to be there.