…perties

The "readSnapshots" middleware function can now look like this:

```
function(request, next) {
  let {
    collection,
    snapshots,
    requestMethod, // 'fetch', 'query', etc.
    requestParams, // object whose shape can vary
    snapshotType,
    agent
  } = request;
}
```

- requestMethod -> method, requestParams -> parameters
- Distinguish methods 'queryFetch' and 'querySubscribe'