Duplicating rundowns unsafe

[Dan-Shields]

When duplicating a rundown the template itemIDs rename the same, causing issues if both the original and copy rundowns are open.

Also, creating a duplicate of a rundown twice will cause only 1 copy to be created which overwrites the first.

I'm creating a PR for this, creating this issue for posterity

[TuomoKu]

I will keep these here as a reminder for a future update. Thanks for pointing this out!