Fix deltas referring to last system saved
If a system is added, it is added to treema at the end of the list of systems. Treema then raises it's changed event resulting in this order being set on the level. The next time a system is added, the first system is in it's correct position and so the delta shows it as moving. This changes ensures we save the correct order in the first instance.
Merge pull request #874 from dpen2000/FixSystemsListDeltaIssue

Fix deltas referring to last system saved