Be consistent with cache_chain names
Ratelimits: Recover if the incr fails

For a miniscule number of requests, the old value
in memcache will fall out after the call to `add`,
but before the call to `incr`. This change recovers
from that scenario.
Add sample_rate param to Stats.event_count
Add stats tracking to sitewide ratelimiting
Don't double ratelimit error responses
OAuth2: Add /api/v1/me/prefs endpoint

Returns the logged in users preferences
Supports a 'fields' parameter for limiting the
response to the desired fields.
Refactor /post/options for re-use

* Create a var with the validators
* Don't always grab langs out of request.POST
* Refactor validation to a separate function
Add PATCH /api/v1/me/prefs endpoint

Allows partial update of the user's preferences
/dev/api: PATCH endpoint with JSON model support