plugin XEP-0167: keep media order when starting a call: media content order is relevant when building Jingle contents/SDP notably for bundling. This patch fixes the previous behaviour of always using the same order by keeping the order of the data (i.e. order of original SDP offer). Previous behaviour could lead to call failure. rel 424

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)