Add authorizations property to route definition and support for third party authorizations plugin

This Pull Request addresses issue #11.  

# Usage / Implementation

- You can optionally add an ‘authorizations’ parameter to each route with a space separated list of route-authorizations (Example: "admin super-admin"). 

    ```javascript
    server.get({url: '/test/method/:data',
       authorizations: 'account',
       swagger: {
         summary: 'Get',
         notes: '',
         nickname: 'getTest'
       },
       validation: {
         data: { isRequired: true, description: 'Data', swaggerType: 'string', scope: 'path' }
       }}, function(req, res, next) {
          res.send( { data : "get" });
       });
    ```

- The authorizations are listed in the swagger resources.json.

    ```
    "resourcePath": "/swagger/test",
    "apis": [
        {
            "path": "/test/method/{data}",
            "description": "",
            "operations": [
                {
                    "notes": null,
                    "nickname": "getTest",
                    "produces": [
                        "application/json"
                    ],
                    "consumes": [
                        "application/json"
                    ],
                    "responseMessages": [
                        {
                            "code": 500,
                            "message": "Internal Server Error"
                        }
                    ],
                    "parameters": [
                        {
                            "type": "string",
                            "dataType": "string",
                            "name": "data",
                            "description": "Data",
                            "required": true,
                            "paramType": "path"
                        }
                    ],
                    "authorizations": {
                        "type": "account"
                    },
                    "summary": "Get",
                    "httpMethod": "GET",
                    "method": "GET"
                }
            ]
        }
    ```

- when swagger loads it will optionally call a third party plugin to verify the api_key (if provided) and user authorizations.

- configuring the third party plugin is done by passing the 'authorizationsPlugin' in the configuration options.

    ```
	restifySwagger.configure(server, {
	    info: {
	        contact: 'email@domain.tld',
	        description: 'Description text',
	        license: 'MIT',
	        licenseUrl: 'http://opensource.org/licenses/MIT',
	        termsOfServiceUrl: 'http://opensource.org/licenses/MIT',
	        title: 'Node Restify Swagger Demo'
	    },
	    apiDescriptions: {
	        'get':'GET-Api Resourcen'
	    },
                authorizationsPlugin: swaggerAuthorizations
	});
    ```