BUG: adding Common Instance Reference Module

Required when Derivation Image Functional Group is present
BUG: pixel spacing and slice thickness duplicated

These should only be contained in the shared functional group
ENH: move the Studies containint other referenced instances sequence to the right place
ENH: move segment identification sequence

Moved to shared functional group sequence, per suggestion from David Clunie.
For now, only one segment is created, and referenced, so no need to carry it
over the per-frame groups.