- 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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