Give the opportunity to manage the service another way

Hey JF, I like runit, but I'm not a fan of the "runit sprawl" that's happening in all the cool community cookbooks. So I'm trying not to inflict that upon you ;-)

Do you mind having this flag, as a way to let people manage the `uchiwa` service their own way in their wrapper?

Another way this could be done is to split all concerns in their own recipe and have default be a simple list of include_recipe's. This way, when wrapping the cookbook it would be possible to include everything except `include_recipe "uchiwa::service"`.

I can re-submit a PR like this, if you prefer.