Removing extraneous closure references in SMS games

#### What's this PR do?
Cleans up the data we're closing over for callbacks in SGCompetitiveStory game flows - creation, joining, starting, playing. In many places we would do...
```
var self = this;
self.response = response;
self.request = request;
```
We did this to have references to models and configs that were previously attached to the `this` object. And we kept it around because we'd also reference the `response` object to send responses back to the client from within callbacks.

This PR removes the closures around the `this` and `response` objects. It also moves the responses to the client out of the callbacks. Responses are sent immediately as opposed to waiting for async processes to complete. (This should further improve throughput.) Any errors in the async processes are logged instead.

#### How should this be manually tested?
I tested by running `npm test` and going through the first half of a test SMS game through Postman.

#### What are the relevant tickets?
Closes #332