Reorganize realtime images

This patch moves the realtime image pages underneath their `/locations/`
url, so to keep location-based items in the correct url paths. Also, we
stop using implicit data files to load in camera url data, and instead
explicitly specify camera urls as data attributes on the realtime image
viewer container.

I really like this new method, and will implement the same data
attribute methods for the charting and location pages (as asked for in
issue #97).