Add views for inbound/outbound browser calls and transfers

[9mido]

https://github.com/TwilioDevEd/voice-javascript-sdk-quickstart-python

https://github.com/TwilioDevEd/browser-calls-django

https://github.com/TwilioDevEd/warm-transfer-flask

https://www.twilio.com/docs/voice/tutorials/how-to-modify-calls-in-progress-python

I would love if django-twilio could have views that would allow a user to type in a phone number using a form text input to call outbound and accept incoming calls from anybody using their browser.

In addition, during either inbound or outbound calls it would be nice to transfer that call to somebody else. Supposedly this is done via entering into a conference call and then leaving the other 2 people alone.