1050450 measure queue

Adds a `rabbitmq_queue_size` utility function plus adds it to the `/services/monitor` page so we can see what the size is any time we want (yay!).

Adds a `record_queue_size` cron job which kicks off once an hour to send the current size via statsd. This way we can see it over time with Graphite.

r?
:+1: