Add restricted_handlers group list config

[rnaud]

What

No very excited about this implementation as this is not using the restrict_to current syntax. But I didn't find a way to access the config values as part of the route class methods.

This also does not work with the help list of routes as it rewrites the same authorized? method

Usage

config.robot.restricted_handlers = {
  "catgif" => [:important_people]
}

Todo

• [ ] tests
• [ ] documentation