Remove the need to use RtpdumpPacket
Because now RtpdumpStream doesn't use the rtpdump timestamp to sync
the stream. Now the sync use the timestamp of rtp packet directly, with
the timebase computed from the framerate/samplerate of the Format.

Also change the static method that create rtpdump MediaDeviceImpl :
it now takes a MediaFormat, so that it can get the clock rate of the
format (used in the timebase).
update doc + clean up