IndexedDB cursor


### Access by cursor
```typevar objectStore = db.transaction("User").objectStore("User");objectStore.openCursor().onsuccess = function(event) {  var cursor = event.target.result;  if (cursor) {    console.log(cursor.key);    console.log(cursor.value.Nickname);    console.log(cursor.value.eMail);    cursor.continue();  } else {    console.log("No more entries!");  }};```