Assigned issue milestone is not properly handled when moving issue between projects

Summary

Moving an issue doesn't behave like "move". What move does is to close the old issue and open a new issue in the destination project. This causes a lot of confusion when using issues with weight and milestones.

As the old issue is closed the milestone's burndown chart is rendered as if the issue was solved and the remaining milestone weight is reduced. The new issue doesn't inherit the milestone property and must manually be added to the milestone again.

Steps to reproduce

1. Create new issue in project
2. Assign weight and milestone to issue
3. Move issue to other project
4. Go to the milestone view. The old issue is still assigned to the milestone and is now closed. Burndown chart and milestone total weight are now wrong.