Add $pushItem(), $getItems(), & $getObject() to Storage.prototype

[avand]

pushItem(k, v) {
  var a = getItems(k);
  a.push(v);
  localStorage.setItem(JSON.stringify(a));
}

getItems(k) {
  var a = getObject(k);
  if (a == null) a = [];
  return a;
}

getObject(k) {
  return JSON.parse(localStorage.getItem(k));
}