* feat(multi-stream-support) Handle SDP munging for multiple local/remote streams/ep.
A new SDPSimulcast class is added for handling SDP munging for local and remote descriptions to handle multiple streams for both local and remote endpoints. This new class will be used only for unified plan implentation. The sdp-simucast npm package will be used for plan-b and deprecated later when all the clients switch to unified plan.

* fix(build) fix building with TS code

Use the Babel preset for the webpack bundle since Babel 7 already
understands TS and ts-loader uses tsc instead, which we configure
differently.

* squash: Add unit test and address review comments.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>