Add a full-size preview facility

[ohnotnow]

It would be nice if there was a way of previewing a full-size copy of an image. I sometimes have two very similar images with slightly different (and oh-so-funny $internet_points++) captions but it's quite hard to tell them apart at the moment. Being able to alt-click or whatever on an image to get a proper preview would be really useful.

[lostdesign]

Will defo be added, giving more info / insight with stats and being able to change filename and what not. Same with showing filenames on hover. Currently figuring out a good UI, but much needed indeed.