Refs #969 - Proxy-side changes for serving templates from the proxy

An update to @GregSutcliffe's original PR (https://github.com/theforeman/smart-proxy/pull/100/files). Ports his original feature to the new plugin api.
@sodabrew, @GregSutcliffe 
Updated to use ForemanRequest (#223) as suggested below. This makes the user define 
foreman_url,
foreman_ssl_cert,
foreman_ssl_key 
in the main settings.yml to use ssl