Add support for statuspage proxy usage

[drhey]

I ran into the issue of not being able to use a proxy with sensu-plugins-statuspage (which relies on the Redphone module). I've added code to that project to support basic proxy usage (address and port). I don't currently require a username and password so I've not added it in - but it would be trivial.

My commits here would allow for the handler-statuspage.rb plugin to pass off the vars proxy_address and proxy_port to statuspage.rb (which is instantiated by handler-statuspage.rb) and then be utilized by helpers.rb (if they're set and picked up).

I've tested and verified that these changes work in my environment

[drhey]

Want to do just a little bit more testing

[drhey]

My testing confirmed my changes are correct.