Make it possible to download images with a shortcut

[polm]

I feel that there should be a way to download images using keyboard shortcuts - like using the link shortcut, but instead of presenting options for every anchor element present one for every img element.

[deiga]

I've been investigating this for a little while and I'm beginning to think that it's not possible.

JavaScript doesn't have tools to actually invoke any kind of save dialog, at least not client-side.

[deiga]

This PR lays the foundation for this feature.

basically what it would have to do is:

• select all images on the page
• apply similar functionality as .wrap()
  • $('img').wrap('<a href"'+href+'" />')
• then hilight only links generated by this
  • maybe adding a class of data attribute to the generated links and only hilight those
• then call the download LinkHint functionality