ratelimit: Improve enforcement page text.

This is intended to be more clear about what's going on when the
ratelimit's enforced and what the user's options are.
ratelimit: Remove reddit-dev mailing list link from throttle page.

It's probably best for users not to send their IP address to a public
mailing list.
Add markdown.less
Remove markdown styles from reddit.less and wiki.less
Most of them, at least.
Feature-flagged new markdown styles.
Actually fix the disabled 'new campaign' bug.
Fix calculation of total bid and impressions on edit_promo page.
Cleanup new markdown styles.
Simplify markdown style changes.
Fix thumbnail in creative editor overflowing container.
Add option to create a campaign without closing the editor

Stop gap solution until multiple targets can be added for a single
campaign.  Allows people to set up many similar campaigns without
having to start again from scratch.
Add React.js
Add Campaign Creator component.
Fix campaign editor label width.
Fix long date ranges possibly using an extra day in inventory calculations.
Pretty print impressions.
self-serve: Fix campaign bid calculation on frontend.

Fixes a rounding error causing the UI to sometimes display an inaccurate
maximum campaign size.
self-serve: Fix house ad creation.
self-serve: Remember user's requested bid and dates when keeping campaign editor open.
self-serve: Remove feature flag for 'keep open' feature.