LP#1726568: expose circ lib and owning lib fields to spine/pocket labels

LP#1726568: expose circ lib and owning lib fields to spine/pocket labels

This patch fleshes the item circulation library and owning library
fields so that spine/pocket labels can include the short name or
full name of the OU rather than just the ID.  As a consequence, the
following fields are now available for label templates:

* copy['call_number.owning_lib.id']
* copy['call_number.owning_lib.shortname']
* copy['call_number.owning_lib.name']
* copy['circ_lib.id']
* copy['circ_lib.shortname']
* copy['circ_lib.name']

If, for some reason, existing label templates intentionally use
copy['call_number.owning_lib'] or copy['circ_lib'] to include the numeric
ID of the OU on the label, they will need to be replaced with
copy['call_number.owning_lib.id'] or copy['circ_lib.id'] respectively.

To test
-------
[1] Apply the patch.
[2] Open the print labels window for an item and try including one
    or more of the new fields listed above; verify that the current
    value is displayed on the label preview.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>