Collapsing `message.text`, `postback` and `quick reply` events into `text` (#24)
Collapsing `message.text`, `postback` and `quick reply` events into `text` (#24)

Closes #15

## Why are we doing this?

Per #15, this unifies the handling of `message.text`, `postback`, and `quick reply` messages to improve the user experience.  From the original issue:
> Practically, the whole point is the user can send the same text multiple ways and get the same response, so having a special check for the origin shouldn't be necessary. In addition, the raw message is available so it can always check the origin with a little extra code.

## Did you document your work?

Yes, the `README` has been updated.

## How can someone test these changes?

* check out the `text-event/#15` branch
* run the chat bot, `npm run dev`
* send text, start a quiz, etc. and observe that the behavior has not changed from `master` despite the logical change under the hood.

## What possible risks or adverse effects are there?

This makes it slightly more difficult to process `message.text`, `postback` and `quick replies` differently, but as mentioned in the original issue, this is deliberate. The developer should be thinking critically about why the application needs to process these events differently than `text`.

## What are the follow-up tasks?

* updates to `replyToEventText` and the `text` event handling to deal with source differences more cleanly?

## Are there any known issues?

None identified.

## Did the test coverage decrease?

Reduction in complexity yielded a slight increase in coverage, however,`message.text`, `message.postback` and `message.quickReply` events, commented as _deprecated_ are no longer covered.

Before:
```
=============================== Coverage summary ===============================
Statements   : 70.57% ( 235/333 )
Branches     : 64.1% ( 75/117 )
Functions    : 67.86% ( 19/28 )
Lines        : 71.6% ( 232/324 )
================================================================================
```

After:
```
=============================== Coverage summary ===============================
Statements   : 71.26% ( 238/334 )
Branches     : 64.1% ( 75/117 )
Functions    : 70.37% ( 19/27 )
Lines        : 72.31% ( 235/325 )
================================================================================
```
CondeNast/launch-vehicle-fbm