Add Google Hangouts Chat support to Botkit

[ouadie-lahdioui]

Hi everybody 👋

This PR adds support for Google Hangouts Chat platform into Botkit 🎉

Developers will be able to make hangouts bot simply like that :

var controller = Botkit.googlehangoutsbot({
    endpoint: 'WEB_SERVER_ENDPOINT',
    token: "YOUR_TOKEN"
});

Hear users expressions :

controller.hears('new thread', 'message_received', function (bot, message) {
  // Awesome code here
});

And replay with several methods :

• .reply(...)
• .replyAsNewThread(...)
• .replyAsNewThread(...)

I'll make another PR on botkit-docs project to add documentation.

Enjoy

[vmichalak]

In English, there is no space in front of the punctuation marks ; ! ? :

[ouadie-lahdioui]

Done

[peterswimm]

This fixes #497

[guillain]

Works as a charm, thanks guys :-)