/gold/creditgild: Check comment viewing permissions.

Previously, it was possible to generate a payment blob for a comment the
user does not have permission to view (in a private subreddit or
deleted) and then use the creditgild form to see the author and content
of the comment.  This adds a check to creditgild to ensure correct
permissions at display time.

This fixes an information disclosure vulnerability reported by Jordan
Milne (/u/largenocream).
/api/generate_payment_blob: Check comment viewing permissions.

This is not strictly necessary as /gold/creditgild is where the
information leak actually occurs, but checking here should help prevent
future leaks of the same type.

This fixes an information disclosure vulnerability reported by Jordan
Milne (/u/largenocream).
/tb/: Check permissions before redirecting.

When the user is not logged in or has the toolbar disabled, the toolbar
endpoint will turn a link ID36 into a redirect to the submission on
reddit.  This redirect includes the slugified title of the post as well
as the subreddit it's in which could lead to a leak of information from
a private subreddit.

This fixes an information disclosure vulnerability reported by Jordan
Milne (/u/largenocream).
wiki: Remove recursion and fix wiki page list filtering.
Pass fullname on deleted things if we're admin.
memcache: Reduce compression threshold for rendercache.
terminate_campaign: pass location to edit_campaign.
Set default geotargeting country correctly.
CommentTreeStorageV1.add_comments: write parents first.

When assembling a comment tree it's necessary that all comments
are present in parents. Writing parents first ensures this.
POST_submit: add hook for when banned domain submitted.
media: Make hooks for adding scrapers into the mix.
SRMember: Start dual-writing to a dedicated cache pool.

This is one of the most heavily hit rels currently and the hope is that
pulling it out to its own pool will make the main cache more effective
for everything else.  It may make sense to move SRMember to a different
model such as a C* DenormalizedRelation in the future.
Missing RequirementException import
CommentBuilder: add timers.
terminate_campaign: immediately update promote status to finished.
VOrAdminSecret: don't check modhash on GET requests.
CommentBuilder: separate `comment` and `children` handling.
CommentBuilder: delete debug_dict.
CommentBuilder: cleanup logic for selecting candidate comments.
CommentBuilder: move sorting/updating candidates to its own method.