Global graphite sub-namespace

[kvlahromei]

Hi, the plugin(s) work like charm, thank you 👍

As we like to store more than just monitoring timeseries to our carbon / whisper backend, we like to move all the host / services series to a seperate namespace e.g. 'monitoring.. ....'

Unfortunatly it seems that even using GRAPHITE_DATA_SOURCE and _GRAPHITE_PRE, _GRAPHITE_GROUP can't solve this problem, as they are appended after the hostname.

So yould you plz. add an additional global GRAPHITE_DATA_PREFIX to the module config?