Add flag to enable or disable the query page

Puppetboard is an excelent radiator of information, but sometimes
we want to expose information to users we don't trust giving full
access to the PuppetDB query language.

I would reccomend that Puppetboard be run twice. One, with query
enabled, run on a port behind apache login. Another, with query
disabled, run unproxied for the unwashed masses.