Temporary bandaid for top bar breaking various subreddits.

sr_pops has put certain subreddits into the top subreddit list multiple
times. This causes there to be multiple buttons in the srbar. The sort
logic in NavMenu.find_selected short circuited when the lists were of
length 1, but now that they aren't it's dying rightfully on this
attribute not existing on SubredditButton. This is a temporary patch to
help until the sr_pops issue is fixed.
is_banned_domain: remove ip argument.
is_shamed_domain: remove ip argument.
Don't allow shame banned domains for promoted links.
Add link note for banned domains.
wiki: Verify that a user may view a revision on a revision listing.
wiki: Do revision WikiPage lookups in batch.
wiki: Correct parameter highlighting in alloweditor docs.
wiki: Add uri variants for alloweditor.
api_docs: Add a captcha section.
api_docs: Move new_captcha to captcha section.
api_docs: Add /captcha to api docs.
api_docs: Improve captcha docs.
wiki: Use global karma for frontpage wiki.
wiki: Ignore can_submit on the frontpage.