Add improvements to list fields (multiple selections)

The imagelist seemed like a really powerful field to me, but it felt clunky to use when I first tried it out. I've now made it possible to select multiple items, drag them around, and delete in bulk in both imagelists and filelists.

In imagelists you can magnific-ly view images by clicking on the thumbnail.

I think another useful feature (not in this) would be to select multiple items from the server like you can when uploading images.