Show host data if down

# The Problem
In the Web UI if a host goes down, many of the metrics become unavailable. These metrics can be extremely valuable in determining what went wrong. In some cases, these hosts may never come back (such as autoscaling groups through Amazon).

# The Change
Added a variable in the configuration file, $conf['show_host_data_if_down']. When false (default), the additional metrics do not render, and the behavior as it is today does not change. If set to true, the graphs and metrics will render under the host_view page, even if the host is down.