Return errorElem and do not store the Ajax object

* If the Stack Exchange API went offline, this code would fail because `showError()` is not returning `errorElem`. I added a line to return errorElem.
* Storing the jQuery Ajax object as a variable named `result `was confusing to a student of mine, since the callback method for `.done()` using a variable of the same name. There's no need to store the jQuery Ajax object so I deleted that portion of the line.