Add optional controversial indicator to comment scores

Conflicts:

	r2/r2/lib/pages/pages.py
Make time_listings defensive against bad URLs
Support 'all' in compute_time_listings
Add first cut of feature flags via `r2.config.feature`.
Small feature: auto-restrict subreddit searches (flagged)
Gold Checkout Redesign

This is a full redesign of gold checkout, including new resources for
gilding and creddits, at /gilding and /creddits. Work done in
collaboration by @powerlanguage and @umbrae.

This is primarily a visual refresh, although some flow has changed
(primarily that creddits now have their own endpoint, and there is a
/gold/payment page for finalizing payment which is handier for
analytics).