Add an option to force the client to use only TURN candidates

[jcague]

Description

Add an option to force the client to use only TURN candidates

[] It needs and includes Unit Tests

Changes in Client or Server public APIs

We can now force the client to use a TURN server when publishing/subscribing by setting the next parameter:

room.publish(localStream, {forceTurn: true});

• It includes documentation for these changes in /doc.

[kekkokk]

I suggest to automatically activate this feature after 2 subsequent publish/subscribe fail as it would be probably the only option left to make the call works.

[jcague]

I don't think it's necessary, but we can consider it in the future if we detect multiple cases.

[kekkokk]

I experienced an issue with 2 different customers where their firewall blocked the stun binding request if were made too closely (a sort of ddos protection I think).
I was stuck in a loop where a stream-failed event were fired and tried to re-subscribe. The only option for me was to force that mechanism :(

[kekkokk]

Also, another interesting feature would be dynamically generate ice Servers without breaking the async structure of the process.
I mean, 99% of us is using a third party library to get turn credentials such as xirsys or twilio.
so everytime an user try to publish/subscribe a stream it would be nice to have a place where to put inside an async call to the preferred service which returns an ice config and make the process of publish/subscribe start