Improve Create Ops

Introduce `CreateOp` interface: When creating objects, we sometimes don't know what kind of object we want to create, because the input type may vary. Example is `CopyOp` where depending on what we want to copy we have to create a different output. If we want to copy a `RAI` we currently assume that we want to create a `RAI` which we associate with an `Img`. In the end, however, we want to create a `ImgLabeling` which will be used as target container.

This functionality is required as soon as we want to use `burnIn`.