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.