refactor(speechrecognition): rename directive option `thing` into `reference`

Breaking change: thing options is now renamed into reference

Before:
```
<li ng-repeat="todo in todos" speechrecognition="{'tasks': recognition['en-US']['listTasks'], 'thing': todo}">
	{{todo}}
</li>
```

After:
```
<li ng-repeat="todo in todos" speechrecognition="{'tasks': recognition['en-US']['listTasks'], 'reference': todo}">
	{{todo}}
</li>
```