first pass at AcqSearchService

first pass at AcqSearchService

This adds AcqSearchService, which knows how to produce
a GridDataSource of the appropriate type and default
search parameters and options. This also adds results
components for purchase orders, invoices, and selection lists.
Note that the new results components don't customize
the columns that are displayed.

AcqSearchService is intentionally _not_ set up as a singleton,
and instead is used as a provider by the four results components.
This can be changed if a reason turns up later to have the service
retain some state for the duration of the application session
(as opposed to the duration of the results component; note that this
may mean that the results component will need to embed the search
form component so that it can readily share the grid data source
with it).

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