Sippo-378

New functionality added using Peer Connection GetStats method for both local and remote vumeter. 

Remote Audio (AudioOutputLevel) and Local Audio (AudioInputLevel) are read each 150 mseconds. Values between 0 and 32767 are obtained and classified between 0 and 3 (directly linked to current vumeter view). If at least one value is new, an event "vumeter" is triggered, which will be received by the stack using RTC.

In the future this processing could be improved.

This doesn't seem to be a problem for the browser load, but I'll be watching that during next weeks.