Add displaying of random images for filter sets

Squashed commit of the following:

commit dde6b6b99fec60e9add1e1c8d8f727630c586347
Author: Jonasz Grochowski <tensaioni@gmail.com>
Date:   Mon Aug 18 08:44:44 2014 +0200

    Add displaying of random images for filter sets
Be explicit, there is no such thing as ordered_by(:random)