Added getUserVotes endpoint

Currently uses the newly-fixed getSurveyResults code, which results in output like:
```js
{"5":0,"6":1,"7":0,"8":0,"9":0,"10":1,"11":0,"32":1}
```
The output is exactly the same as getSurveyResults, but limited to just the current user. Is this what we want?

Like before, this is being merged into the sessions branch.