adding common handlers.

server.go

 	return strings.TrimPrefix(urlPath, "/crmfiles/")
 }
 
+func response400Handler(w http.ResponseWriter) {
+	w.WriteHeader(http.StatusBadRequest)
+	str, err := ioutil.ReadFile(GlobalPath.SinglePageEdit + "400.html")
+	if err == nil {
+		fmt.Fprintf(w, "%s", str)
+		return
+	}
+	fmt.Fprintf(w, "bad request")
+}
+
 func response404Handler(w http.ResponseWriter) {
 	w.WriteHeader(http.StatusNotFound)
 	str, err := ioutil.ReadFile(GlobalPath.SinglePageEdit + "404.html")
 	fmt.Fprintf(w, "not found")
 }
 
+func response403Handler(w http.ResponseWriter) {
+	w.WriteHeader(http.StatusUnauthorized)
+	str, err := ioutil.ReadFile(GlobalPath.SinglePageEdit + "403.html")
+	if err == nil {
+		fmt.Fprintf(w, "%s", str)
+		return
+	}
+	fmt.Fprintf(w, "not authorized")
+}
+
+func response500Handler(w http.ResponseWriter) {
+	w.WriteHeader(http.StatusInternalServerError)
+	str, err := ioutil.ReadFile(GlobalPath.SinglePageEdit + "500.html")
+	if err == nil {
+		fmt.Fprintf(w, "%s", str)
+		return
+	}
+	fmt.Fprintf(w, "server internal error")
+}
 func getHTTPRequestQuery(r *http.Request, name string) (value string) {
 	rq := r.URL.RawQuery
 	m, _ := url.ParseQuery(rq)