Activate TURN Server in RSB release

[christianbrb]

Problem

The LC team is currently implementing WebRTC (see PR raiden-network/light-client#1290) and we would like to fully run on Matrix. Currently, the Google's STUN server is used as a fallback.

Solution

From raiden-network/light-client#1331

The recommended matrix TURN server is coturn, and it provides full TURN capabilities, not only STUN (TURN is a superset of STUN which also supports relaying). Here is the official guide for deployment, and when available, is always preferred over the fallback one.

CC @andrevmatos