Fallback images

[rodericj]

We need to have a fallback image incase any of a number of things happens.

1. Image can't be fetched at this time
2. Image URL is not included in the metadata (never set or whatever)
3. Something else?

We had chatted during Coffup today and we're looking to de-emphasize foursquare's image API usage. As a larger initiative to that end we need to implement this fallback. We had the suggestion of using the group image which is certainly possible, however we would need to have #33 or some subset of that merged in.

@mcritz has a concept of "Image of last resort" in which the group image is also not fetch able and this likely needs to be some image that is packaged in the binary. Some Coffee glyph or something: ☕️

[rodericj]

Regarding the point above about #33 being merged in, I'd made #61 and it's been merged in. This is the infra to actually fetch the list of groups. The appropriate image URLs should be in there.