Review process: allow use of arrow keys + other shortcuts

[YvanSG]

Feature
Allow use of left/right arrow keys to move through images in the review process. Offer other keyboard shortcuts to add classifications.

Additional Detail
When reviewing lots of images, it's cumbersome to have to click on the "next" button. Allowing the use of left/right arrow keys to move to previous/next image would make for a smoother use. Not sure if it's possible to do.
Additional keyboard shortcuts would help as well: a = animal; e = empty (remove all classifications); m = multiple; p = person; etc.