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.