Add ability to add domains as facebook instances

- Facebook Insights data can be recorded for domains: likes and like
  button impressions are recorded

- Facebook domain instances have a different dashboard than user and
  page instances; there's just one dashboard for now

- Google Chart Tools is used for visualization so this depends on issue
  #1068 being merged first

- Add a customDefaultDashboardModules method to the DashboardPlugin interface
to optionally add additional modules the default dashboard for an
instance.  Modules are defined as MenuItems containing Datasets.

- Add Domain Metrics module to default dashboard for facebook domain instances.