Move (un)mark_as_nsfw Moderatable->Submission.

The behaviour of marking as NSFW is specific to Submission.
Comments (which also inherits from Moderatable) cannot be
marked as NSFW.
Don't raise exception if user is author of post.

It's possible to (un)mark as nsfw if you're either a mod
of the subreddit or author of the submission.
Handle new dataformat of subreddit list.
Handle non-public subreddit contributors edge case.

Accessing a subreddits contributors require user/pswd access for
public subreddits. For non-publc subreddits (protected/private)
only access is required.
Also evict rising listing after approve/remove.