Disabling input text in the presence of buttons should be optional

[hamzaed]

There are scenarios where input text should be disabled but still there are others where both button and free text can coexist.

I suggest to add support of this in xatkit-react-platform (i.e., the bot developer should choose to have both or just the buttons). The bot message object should include a new field telling whether the input text has to be disabled.

Related issues: #26

@gdaniel if you could take care of the xatkit-react-platform part, I can implement this in the widget.

[jcabot]

I'd for now focus on changing the text that it's displayed (from "type a message" to "choose a response". Having the free text together with the buttons has some strong implications on the intent matching part.