Add dashboard folder and graphite dashboard to doc

Add dashboard folder and graphite dashboard to doc

Create a dashboard folder to hold HTML files that provide
dashboard views into various parts of neutron.  This allows
the dashboards to be "living code" rather than frozen in
amber via shortened URLs.

The first dashboard example is a simple HTML file that
shows thumbnails of graphite plots of all neutron jobs
in the check pipeline.  Clicking a thumbnail brings up
the larger graphite plot page.

Change-Id: I47e7718c2aae41c8308fd331377984e47a892294
Signed-off-by: Ryan Moats <rmoats@us.ibm.com>