LP#1653001 webstaff: Holds pull list sortable columns

LP#1653001 webstaff: Holds pull list sortable columns

Retrieve holds for the pull list via the canned "ahopl" pull list IDL
class.  This lets the grid fetch the data via canned flattener query,
supporting server-side sort/limit/offset options.

To retain all previous UI behavior, primarily editing hold attributes
(e.g. notification prefs), hold details for each hold have to be fetched
(and cached) in addition to the main grid data.  The grid renders and
sorts the flattener data, then grid actions act upon the fleshed hold
details data.

Commit also includes:

1. Added some missing IDL links for the "ahopl" class.
2. Micro-optimization to egGrid to exit early when an invalid IDL path
   is provided.

Signed-off-by: Bill Erickson <berickxx@gmail.com>