Handle spaces in graphite metric names

Incoming graphite metric names can contain spaces, for example `jvm/JvmMetrics/GcTimeMillisPS Scavenge` or `jvm/JvmMetrics/GcCountPS MarkSweep` coming from Ganglia. This caused exceptions(number format) which, even though they were caught, seemed to have prevented expired events from being streamed. I didn't get any respective log entries before this fix and get plenty now.
I am a Clojure beginner which is why I left out stuff that I didn't understand and didn't seem to have an effect(namely when-let and ^String). Let me know if I should change something.