Added the add_cookie feature

Added test cases to check cookies in WSF_RESPONSE-
Added mock classes use for test cases.

library/server/wsf/tests/src/wsf_service_null.e

@@ -0,0 +1,23 @@
+note
+	description: "Summary description for {WSF_SERVICE_NULL}."
+	author: ""
+	date: "$Date$"
+	revision: "$Revision$"
+
+class
+	WSF_SERVICE_NULL
+
+inherit
+
+	WSF_SERVICE
+
+
+feature -- Execute	
+	execute (req: WSF_REQUEST; res: WSF_RESPONSE)
+			-- Execute the request
+			-- See `req.input' for input stream
+    		--     `req.meta_variables' for the CGI meta variable
+			-- and `res' for output buffer
+		do
+		end
+end