Bugfixes for RtpPacketQueue and ability to record both Opus and PCMU

There's a number of bugfixes for the RtpPacketQueue that I submitted yesterday:

1. Simplify the push routine; no need to check for an empty queue.
2. Do not insert duplicate samples into the queue.
3. Do not bother inserting a sample that has a lower sequence number than what we've already popped.

There's also the ability to record both PCM and Opus in external output.  Depending on what data it's receiving, it'll automatically do what it needs to do.  Opus is still not enabled in the project (although that's a one-line change in SdpInfo.cpp at this point)