Testing and improving imgur onebox

Made sure that static pages don't get matched, and don't get a cute kitten instead of url. To do this, I added a tests reproducing those situations, and also test reproducing first behaviour

PS. I tried to follow the direction to squash the commits, but all that seemed to do was add a commit by Jeff to my branch, not giving me oppertunity to squash my commits. I will try to find out how I should do that later.