Add tensor copy operations with region support

[Crydsch]

This PR adds the operations OpTensorCopyRegion, OpTensorSyncRegionDevice and OpTensorSyncRegionLocal. They behave similar to their non Region counterparts, but support copying only regions of a tensor.

I have also added a Test, illustrating their use. Each tensor is accompanied by a region (src, dst, size) to be copied. For the two sync operations this relates to each given tensor itself. For the copy operation this relates to the source tensor.

It is based on PR #329 and PR #331 so their commits are currently included as well. If they get merged I can rebase this PR.