Allow multiple copies

Submitted by jEsuSdA

Assigned to Xfburn Bug Triage

When burning a project or an image, it will be a nice idea to add a "number of copies" field.

So, Xfburn can burn a copy, eject, and wait for a new blank disk to continue burning.

Thank you for your efforts and nice work! Salu2 de jEsuSdA 8)