Acq: Towards slick integration of granular un-receive in the PO interface.

Acq: Towards slick integration of granular un-receive in the PO interface.

This adds good UI support for lineitem unreceive.  The bulk of this commit,
however, is in middle-layer rearrangements to make it easier to keep track
of changing lineitems and the POs that they belong to in a long-lived client
side interface.  In other words, when you receive an LI in a PO, the LI table
doesn't only hide the receive button, but keeps track of the LI's state
(received or something else) and shows you the proper controls in any case.
Same for unreceive.

Similar thing coming very soon for lineitem details (copies).

git-svn-id: svn://svn.open-ils.org/ILS/trunk@15593 dcc99617-32d9-48b4-a31d-7c20da2025e4