Catch missing keys from cgminer api
Adds some rounding and verbiage to user stats. closes #72
Added ability to specify multiple backend server connections, and changed all caching to use redis instead of redis + database

* monitor_addr is now deprecated, instead use monitor_addrs as in example
* the Blob table is no longer used for anything. It will be removed in the future. All cached values that were stored there are now in the cache proper
* Tasks run periodically to cache all currently online workers for all servers, instead of doing so on a per-address basis
* Scheduled tasks have been split into cache related tasks and db-changing related tasks, allowing a passive version of celery to run for staging
* Workers now display their stratum connection address when connected
Adds forgotten example of how to set stage variable