Fix WebRTC Leaks

[ghost]

Is your feature request related to a problem? Please describe.
I ran a WebRTC test at BrowserLeaks and I found out that RTCPeerConnection and RTCDataChannel are not disabled.

Describe the solution or the user experience you'd like
If possible, kindly disable WebRTC by default or please give us an option to disable it manually.

Additional context
WebRTC vulnerability: https://threatpost.com/webrtc-found-leaking-local-ip-addresses/110803/

Steps to Reproduce:

1. Open DuckDuckGo Privacy Browser App.
2. Go to https://browserleaks.com/webrtc . The test will start automatically.
   If the values for RTCPeerConnection and RTCDataChannel are true, then WebRTC is not disabled.
   

[ghost]

I noticed that this request was a duplicate of #429

[aitorvs]

Hey @ryan451, thanks for reporting this. If you don't mind I will close it in favor of #429