Added Swagger API explorer

Replaces #15 with a standard swagger-ui instance, and removes the api-key, petstore, wordnik buttons.  The sonos API definition is now in [https://github.com/fehguy/node-sonos-http-api/blob/master/docs/sonos](https://github.com/fehguy/node-sonos-http-api/blob/master/docs/sonos) for easier modification.

Set default URL to http://localhost:5005/docs/api-docs.  To change the default URL, edit the /docs/api-docs file and /docs/index.html