Flattened searching: generalized data retrieval via public service

Flattened searching: generalized data retrieval via public service

For a better overview of what this feature is about than what I could
write here, see docs/TechRef/Flattener/design.txt in this commit.

This is the first new feature (as far as I know) to take advantage of
PCRUD fleshing. Very briefly, imagine issuing a query to PCRUD with lots
of arbitrarily deep fleshing, and getting back a set of flat rows with
the fields you need for display/editing/whatever all neatly picked out
as if ready to be displayed in a table or grid-based UI.

FlattenerGrid, which knows how to use this, can potentially replace and avoid
lots of relatively complex (AutoGrid + custom middle layer
methods)-powered interfaces.  AutoGrid interfaces that just work with
one fieldmapper class at a time, more or less, can just keep doing what
they're doing. Little or no advantage to switcihing to flattened data
in that case.

FlattenerGrid is CRUD-complete and has lots of the same features as
AutoGrid, where they make sense, such as the line numbers, checkboxes,
the columnpicker, multisort, etc.  Sample instance at
Open-ILS/exmpales/flattener_test.tt2 .

Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>
Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Mike Rylander <mrylander@gmail.com>