Image size selector

At the moment nothing helps to figure out that an image can be requested in a different sizes. There should be some kind of UI components that helps to create the urls and embed `` tags for different sizes. The url and the embed code should be copy-able to the clipboard just like github has a button to copy the SHA1 hash of a commit.

The issue names no files, tests, or entry points. Begin by locating the image display UI and the code that produces image URLs; define the required size choices, URL and embed outputs, clipboard behavior, and a way to verify the completed interaction.

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