publish metric creation events

[chrismd]

Implement some method in carbon-cache to send notifications (via AMQP?) whenever new metrics get created.

AcidTonic's comment from original thread:

I'd propose a hook mechanism through the python graphite API. Importing the
API then calling some function to register my script as a listener. Then I
can basically define a callback to be called with the first datapoint and
it's schema object, first value, and time as arguments. My callback could
then connect into my django db and make my models for the new data and make
the graph models show up on my users dashboard.

[Michael Leinartas (mleinartas)]

Migrated to Github: https://github.com/graphite-project/carbon/issues/80