Cycling Raptor

Change the way queue metrics are initialized (#44)

* There are now default metrics, so the queue does not panic in runtime.
* The service name label of the metrics can be easily switched by calling `SwitchMetricsServiceName`, (executed binary name by default)
* `Setup` function is renamed to `SetupTables` because that's what it's supposed to do.
* Use queue metrics like in HTTP middleware