Add HTML5 Drag & Drop upload to Field file

I believe this is a duplicate of #625958: Support Uploading Multiple Files for HTML5 Browsers via #multiple attribute.

Hey @droplet. The other issue definitely didn't solve this. Perhaps this should implement the recommended design from http://groups.drupal.org/node/283223#File_Field?

I've mentioned it a few times before, but this design requires some clever coding to hide the actual file field itself. Hiding an input type="file" requires quite a bit of work last time I investigated this. Additionally, I'm not sure that mock is really the best idea considering users *expect* to be able to click on a browse button, especially on devices that don't have drag and drop at all (tablets and phones).

tag

I would much prefer implementing http://groups.drupal.org/node/283223#File_Field instead of copying what WordPress does.

@quicksketch The design offered offers the ability to both, add using a button and/or drop in the dropable area. I am not very concerned with replacing the traditional widget, which pretty much all major systems (gmail, facebook) override. With that we should handle both usecases you outlined.

Marked this one as duplicate of #2113931: File Field design update: Upload field.