Avoid having non-coherent metrics sent to Graphite

Imagine having the two following metrics "foo_bar" and "foo.bar". Two different stats are computed for each of them, and then, the paths clash when sent to Graphite. Indeed "foo.bar" will be sanitized as "foo_bar".

Also, the sender was using `configuration.core.charset` which is a non-sens. The Graphite protocol only accept one and only one encoding.