[plugin] image preview in popups

[tyrasd]

images (for example from mapillary) that are linked to osm objects could be displayed as a small preview image in the popup. This should be optional (opt-in), since not everyone might want to have this feature active all of the time (it could be distracting in some use-cases and/or the associated additional traffic to fetch the images might be unwanted). At the same time the feature should be relatively easy to discover and activate (e.g. by having a small icon/button besides the image tag).

[cbeddow]

This is an example link to a thumbnail: https://d1cuyjsrcm0gby.cloudfront.net/6hmJoqsSNucA1MGIuvPUzw/thumb-320.jpg

It is in the format of https://d1cuyjsrcm0gby.cloudfront.net/<image_key>/thumb-320.jpg

320 can also be changed for 640, 1024, or 2048. For example: https://d1cuyjsrcm0gby.cloudfront.net/6hmJoqsSNucA1MGIuvPUzw/thumb-2048.jpg

I think it's nice to have an option to show the images at 320px width, and possibly to enlarge (maybe a fullscreen icon like this: http://vocedi.com/static/vocedi_com_theme/img/fullscreen-icon.png), but a click on photo, or click on link icon to open in Mapillary.