Fix mutation of parent extra_page_classes in BrowseController.

This caused the controller to eventually accumulate both the .top-page
and .controversial-page classes for every request since the parent
class's structure was being mutated.
Remove obsolete .cname body class.
spotlight: Only display loading placeholder on the front page.

Subreddit listings often don't have targeted ads, so the previous
default behavior of reserving space usually caused flicker.
Reserve space for the spotlight box on /r/all to reduce flicker.
Listing suggestions: don't suggest the multi you are on currently.
Clean up unused gold partners string.
Add priorities to PromoCampaign.
Remove input names from promotelinkform so they aren't POSTed.
Set default bid when creating new campaign.
Update make_spotlight docstring.
Delete sr_discovery_links.
get_promo_traffic: Handle case with clicks but no imps.
Vote details:  refactor out decoding
Gold goal popup: add yesterday's progress
Deleted link author: add right margin
Listings: use default limit if no pref_numsites

Currently if the user's pref_numsites value is None (very old accounts
that have not changed their preferences), listing pages return all
items, and any hot listings with a sticky crash. This uses the default
page size if the user has not set their own default.
Campaign 'override' attribute can't be boolean.
Add hooks into comment/vote endpoints.

This stuff is needed for the server naming subreddit overrides.

Would love to see it replaced with custom Thing subclasses in the
future.
Remove Google Checkout from gold payment options.
Track subdomains in GA.