Add Gdash role class; apply to tungsten

Settings mostly reproduced verbatim from misc/graphite.pp, with some defaults
omitted and 'whisper_dir' removed (see <https://github.com/ripienaar/gdash/issues/91>).
I'll remove misc/graphite.pp when the migration is complete.

Change-Id: I750de1768943288a86a98b94cbd1f90954563d80