Add support for more RTCP packets

[jcague]

WebRTC now supports different RTCP packets, following the RTP/SAVPF profile:

• Temporary Maximum Media Stream Bit Rate Request
• Semantic Loss Tolerance
• Temporal-spatial trade-off request
• Rapid Synchronisation
• Client-to-Mixer Audio Level
• Mixer-to-Client Audio Level

[lodoyun]

Since 21d99a8 lynckia forwards RTCP messages in OneToManyConnections so we get some of the advantages from RTCP.
There's still work to do in term of using the information receive and not only forward the messages. However, general behavior is better, more so in connections with packet loss or low bandwidth

[jcague]

Definitively we'll need to add support for more RTCP. But it makes more sense if we then open bugs related to the functionality they provide more than the action itself.