Bug 27403: (follow-up) Make basket toolbar and table header work together

Bug 27403: (follow-up) Make basket toolbar and table header work together

The fixed header option for DataTables does the same thing that the
hcSticky jQuery plugin does for us on toolbars, so I've gone through the
templates looking for places they might conflict.

On the acquisitions basket page we can add a special class,
"fh-fixedHeader," to the sticky toolbar to tell DataTables that the
table header should float *below* the toolbar.

To test, apply the patch and go to Acquisitions.

- Locate a vendor and a basket for that vendor with multiple orders.
- Adjust the browse window height if necessary to trigger vertical
  scrolling.
- Confirm that as you scroll down the toolbar (with buttons "Add to
  basket," "Edit basket," etc) sticks to the top of the browser window.
- Confirm that as you continue to scroll, the table header sticks below
  the floating toolbar.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>