Add support to drag selected images to external applications

[StableLlama]

Closes #264

[jhc13]

Do you have some examples of external applications that this can be used with?

[StableLlama]

Do you have some examples of external applications that this can be used with?

Any that accept image files to be dragged to them.

E.g. I'm using it for GIMP. But it's also working with the web browser (e.g. when you want to upload it somewhere, like a Huggingface spaces to try it out)