ESS-1632: Offer Buffering and Double Renegotiations

[ishannaithani]

Purpose of this PR:

Needed for : New MCU and P2P

• When a peer offers it can call createOffer to generate a SDP offer and but use setLocalDescription immediately. 
• The peer will send the said created offer to the remote peer via SIG
• The remote peer will set the offer and send an answer back to the offering peer
• The offering peer, after having received the answer will now call setLocalDescription with the buffered offer
• On success of setting localDescription with the buffered offer, the peer can now call setRemoteDescription with the answer received

Nice detailed diagram by Miniruwan Mangala at https://bitbucket.org/TemasysCommunications/skylink-signalingspec/src/new-mcu/

See ESS-1632 for more details.