add AsgShallowCopyAlg, remove SysCopyHandle from AsgSelectionAlg

This goes back to an old discussion that in principle AsgSelectionAlg should not have a SysCopyHandle, as it doesn't introduce new momentum systematics. The reason it has one currently is that if there is a selection before the correction algorithm it does need to make a shallow copy that can then subsequently be modified at will.

The solution implemented here is what we discussed back then: To implement an algorithm that does nothing more than make a shallow copy (based on the view container algorithm and the copy mechanism from SysCopyHandle) and schedule that before AsgSelectionAlg as needed.