max80.js: change fillin() and load() to use CSS selectors

Especially for translation, it will be more useful to be able to use
CSS selectors to change multiple entries of the same class.

esp32/www/com/max80.js

@@ -83,12 +83,11 @@ function loadform(form, url) {
 	.catch(() => {});
 }
 
-// Replace HTML element contents with the contents of a map
+// Replace the contents of selected HTML elements based on a map with selectors
 function fillin(map,html)
 {
     for (const [key,val] of map) {
-	var e = document.getElementById(key);
-	if (e) {
+	for (var e of document.querySelectorAll(key)) {
 	    if (html)
 		e.innerHTML = val;
 	    else