508 images in submission legend

Closes #508, and fixes a map error discovered in testing.
To test that this feature works, navigate to http://localhost:3000/hkicameroondata/48/328 on a zebra instance hooked up to stage.ona.io, and click on the submission in Kathmandu. An image should load in the legend.

The reason to test with that particular instance is that the photo for it was saved directly to stage.ona.io via enketo.