Move offer from stack to heap

[sirknightj]

What was changed?

• 1915 was rebased to latest develop, see the original PR for details.

• The remote description's lifetime is now shortened to only when it's needed. It does not live throughout the entire PeerConnection anymore.
  • In master mode, it lives between setRemoteDescription (receive offer) and createAnswer
  • In viewer mode, it lives between setRemoteDescription (received answer)
  • If for whatever reason, the user does not call the method in charge of freeing this memory, it is cleaned up in freePeerConnection.
• SDK-Application API remains unchanged. SDK handles the memory management for the SDP offer.
• Add CHK_LOG_ERROR and ENTERS() and LEAVES() in missing places in PeerConnection.c
• Add missing free's to make sure remote description is freed even when there's a goto cleanup due to an error.
• Add missing null checks to some callocs (failed to allocate due to oom)
• Add additional null checks to some methods.

Why was it changed?

• Reduce memory while the peer is connected. After responding to the remote sdp, it is not used anymore.

How was it changed?

• PeerConnection struct (SDK internal) stores a pointer to heap instead of it living within the struct.

What testing was done for the changes?

• Unit tests pass.
• Check valgrind output of master and viewer samples with the JS page: All heap blocks freed -- no leaks are possible.
• Checked the master sample frames (H.264/Opus) on Ubuntu and Mac with the JS viewer and was able to see the video and hear the audio.

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[unicornss]

Refactor to allocate remote session description on heap.