MXS-1220: Add self links to all resources

A self link to the resource itself provides a convenient way for the
client to request a resource, modify it and call the self link to update
it. This removes some of the burden on the client to keep track of the
resource links by placing these in the resource itself.

server/core/maxscale/httprequest.hh

@@ -162,6 +162,10 @@ public:
     }
 private:
 
+    /** Constants */
+    static const std::string HTTP_PREFIX;
+    static const std::string HTTPS_PREFIX;
+
     std::map<std::string, std::string> m_options;        /**< Request options */
     mxs::Closer<json_t*>               m_json;           /**< Request body */
     std::string                        m_json_string;    /**< String version of @c m_json */