Bug 23101: Hide action buttons on contracts if user lacks permission

Bug 23101: Hide action buttons on contracts if user lacks permission

When the user doesn't have superlibrarian, full acq or
contracts_manage permission, don't show buttons for editing
and deleting contracts.

To test:
- Create a vendor with a few contracts
- Create a staff user with
  - superlibrarian = can view edit/delete contracts
  - full acq perms = same
  - without manage_contracts = can view, but action buttons are gone
- Make sure the sorting of the contracts table works in all cases

Signed-off-by: Holly Cooper <hc@interleaf.ie>
Signed-off-by: Bouzid Fergani <bouzid.fergani@inlibro.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>