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.
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- add a `jingle_preflight_info` method in the Jingle Application model to handle this kind
of information
- XEP-0353 is calling `jingle_preflight_info` when a `ringing` message is received
- XEP-0167 use this information to send a `ringing` info to frontends
- XEP-0166: add `jingle_preflight` and `jingle_preflight_cancel` methods to prepare a
jingle session, principally used by XEP-0353 to create and cancel a session
- XEP-0167: preflight methods implementation, workflow split in more methods/signals to
handle UI and call events (e.g.: retract or reject a call)
- XEP-0234: implementation of preflight methods as they are now mandatory
- XEP-0353: handle various events using the new preflight methods
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