fptf 2.0.0 checklist

Things we need to work on for fptf 2.0.0:

• add a code of conduct (?) #36
• decide on / implement stopover type #35
• [ ] decide on major design changes proposed in #61
• [ ] add the canceled attribute #27
• decide on wether to "forbid" redundant origin/destination information in journeys #34
• [ ] decide on proposed information up-to-dateness attribute #43
• [ ] decide on modes / products #62

This issue's intention is not to rush publishing the next version, it should just provide a neat checklist for what we still have to work on.