Bug 28565: Move the sysprefs to a reusable sub

Bug 28565: Move the sysprefs to a reusable sub

This patch moves the big sysprefs list to a sub. Behavior shouldn't
change.

To test:
1. Run:
   $ kshell
  k$ prove t/db_dependent/UsageStats.t
=> SUCCESS: Things work as expected, no changes.
2. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>