Bug 11798: fix problems with column sorting and row visibility in invoices table

Bug 11798: fix problems with column sorting and row visibility in invoices table

1) Sorting on "Billing date" (functionality introduced by bug 10794)
doesn't work properly any longer after bug 10401 was pushed (another
side-effect being that "Vendor" column is currently not sortable
at all).
2) Only "top ten" invoices are always displayed in the table, and it's
not possible to change that without missing top/bottom DataTables
pagination bars.

This patch fixes sorting for "Billing date" &  "Vendor" columns
in invoices table and restores the ability to see all table
rows/search results (not just "top ten").

Test plan (you'll need to have 11+ invoices with various billing
dates entered in the system):
1) apply patch,
2) view the Acquisitions invoices page (acqui/invoices.pl), do some
search (= as broad search as possible) and confirm that "Billing
date" and "Vendor" columns now do sort correctly,
3) in situations when there are more than 10 search results, they
should all be visible in the invoices table.

NOTE: Generating invoices is a painfully convoluted mess.
      All my "Billing date" entries were blank, so was not
      able to confirm Billing date issues. However, Vendor
      sorting issues, seeing more than 10, and in my bizarre
      initial case the non-visible checkboxes were all fixed.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>