enhance event notification API, so that there can be several listeners, and each listener can decide to receive event synchronously or asynchornously.
Add a new player/resampler/mixer in AudioStream, so that it is possible to play sounds to local speaker, in call or idle.

This was due to a missing filter call to setup the 
preview orientation in the stream establishment.

set default video renderer filter to X11 for linux (openGL video renderer stays black on many computers...)

- trick the sampling rate to 16kHz for the complete graph when use of AECM is requested
- leave RTP send/rcv filters at 48kHz as requested by opus RTP payload RFC

-factorize audio_iterate, video_iterate, media_iterate
-add up/down bw stat to MediaStream
-fix bitrate controller driver for opus
-add Mediastream tester

* workaround hardware bug on Galaxy S3 mini, where audio recorded is bad at 44100 and 32000 Hz.
* allow native sound system to work on Android 4.3 (few API changes)
* move android_echo.* files to a more generic implementation, so that it can be used on other OS as well.

It has to be ignored.

fix recv buff size of RTP packet: should be 1500 at minimum, regardless of configured mtu (ms_get_mtu()).

Add API to get list of video encoder configurations and to set the video encoder configuration to use.