Bug 23391: Hide finished ILL requests

Bug 23391: Hide finished ILL requests

Currently, the main table of ILL requests will display all ILL
requests in the database, regardless of their status. For libraries
with active ILL this quickly leads to a lot of requests being displayed,
and the main page of the ILL module taking a long time to load. This
patch proposes to fix this by introducing the ILLHiddenRequestStatuses
syspref, which can take a pipe-separated list of ILL statuses that
will be hidden from view in the ILL module. This means that the
only way to find a hidden request will be through a report.

To test:
- Apply the patch and make sure the atomic database update is run
- Make sure you have a few ILL requests, with at least two different
  statuses
- Check that all requests are still displayed in the main table of
  ILL requests
- Add one of the statuses* you have in your database to the
  ILLHiddenRequestStatuses syspref, reload the ILL module frontpage
  and verify that requests with the given status are not displayed
- Change the syspref to another status and verify requests with
  that status are now hidden
- Change the syspref to hold both statuses, separated by the pipe
  symbol (e.g.: A|B). Verify that no requests with the given
  statuses are now displayed
- Run the ILL REST API tests, e.g.:
  $ sudo koha-shell -c "prove t/db_dependent/api/v1/illrequests.t" kohadev

* = The ILLHiddenRequestStatuses syspref should hold status codes, like
"REQ" and "NEW", not their human readable counterparts.

Signed-off-by: Andrew Isherwood <andrew.isherwood@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>