Order to-be-created relations by dependencies in the changeset

[mstn]

This patch fixes #3208. In details:

• New relations are ordered in the changeset so that children appear in the file before their parents.
• Circular dependencies are not ordered because it is not possible. In this case, an osmChange will be generated, but the API will return an error. Ideally, the user interface should prevent users from creating circular dependencies. Hence, this case should not happen.
• The bug is specific to creations. I do not think that we need a similar fix also for modifications and deletions.

Hope everything ok. Otherwise please let me know! :)

[bhousel]

Thanks @mstn! This looks really good 👍
I will try it out over the weekend...

[bhousel]

I tested this out and it does reorder the relations.. Thanks again!