Overhaul scraper_q processing.

This is primarily about removing the dead old scrapers in favor of a
streamlined oEmbed-based system.  The new embed.ly scraper uses their
Service API to determine which URLs can be scraped through them. This
removes the giant list of domains and regexes in the code and makes the
scraper_q proc always have the latest list of scrapable domains.
Fix media embeds on promoted links.
Use HTTPS for all communication with embedly.
Update contest mode help tooltip.
Recommend X-Modhash usage in the API docs.
Remove semicolon.
Move left bar collapsing to server-side preference.
Add explanation on how to hide default listing chooser display.
Move sample multis list to live config.
Add gold perks listing chooser tab.
Add tab to listing chooser for multi explore subreddit.
utils: Remove obsolete cmd_utils module.
cache: Remove obsolete PyMemcache implementation.
Add health check for caches.
Make scraper_q start fetching secure media objects.

These are media objects that can be embedded safely in an HTTPS page.
Only a handful of services support this through embedly right now, and
that list is hardcoded until embedly's service API is updated.
health: Use one second for the timeouts.
Collect simple vote count stats.
See you later RewriteMiddleware.

This appears to only have been be used for obsolete .js URL forms of
widgets.
Remove obsolete .wired views.
Move CHEATER error into a flag.