Add Matlab plotting script generator to neteq_rtpplay

This change adds an option to have neteq_rtpplay generate a Matlab
script. When executed in Matlab, the script will generate graphs with
the timing information from the test run.

The script is generated when the flag --matlabplot is passed to
neteq_rtpplay.

The CL also adds better checking and reporting about packets discarded
in the process of finding out the initial sampling rate.

Bug: webrtc:2692, webrtc:7467
Change-Id: I805e7c83b82533142b6e74bf065506e3d60a8170
Reviewed-on: https://chromium-review.googlesource.com/541276
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Original-Commit-Position: refs/heads/master@{#18680}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 0bc0ccdc43ced607e58adf33023d4f7ee548446b
3 files changed