Change next media behavior when not inside a thread

[toniz4]

When opening a video or image from a thread, when not inside it, there is no next or previous media. I think that it would be nice if by clicking in the thread photo/video, the next media would be the photos and videos inside the thread, it would make it nicer for those that just wanna see the photos and videos of a thread. This is the behavior found in read chan.

Thanks for developing this application.