Move Photo Overlays to their own section

[quincylvania]

It's weird that three of these have the same name, with the differentiating part put in parentheses. I propose placing this list in its own section organized like this:

Photo Overlays

• Bing Streetside
• Mapillary
  • Traffic Sign Overlay
• OpenStreetCam

[BjornRasmussen]

I think that a checkbox for "360 images only" would also be super useful - see this photo:

Clicking on 360 images gets very hard without zooming in a lot (Click on the image above to see the area in iD).