Changed notification API for renegotiating streams

Ignore-this: edaa8e83c1c3005aaaab1d61d7e9c71e

- renamed SIPSessionGotProposal to SIPSessionNewProposal
- renamed SIPSessionGotAcceptProposal to SIPSessionProposalAccepted
- renamed SIPSessionGotRejectProposal to SIPSessionProposalRejected
- renamed streams to accepted_streams with SIPSessionProposalAccepted
- renamed streams to proposed_streams with SIPSessionProposalRejected
- SIPSessionDidRenegotiateStreams now has added_streams and removed_streams
  instead of action and streams

darcs-hash:20131104102415-b22ec-27c66a891176bdab1992e4808a73a7efdf077214
Renamed streams to proposed_streams on SIPSessionNewProposal

Ignore-this: fff3d6fb4a002d5e20e106d2f957cad8

darcs-hash:20131105123855-b22ec-9c41bb566473a478ffcc0dce8ed9960e26344fc8
Renamed streams to proposed_streams on SIPSessionHadProposalFailure

Ignore-this: 2ad2b39053cf8e7ed43041f26da9ce4b

darcs-hash:20131105123930-b22ec-e8bca80c8765e915237fd11f1da27fa4d805a91d