Bug 18837: Add ILL Unmediated syspref stuff

Bug 18837: Add ILL Unmediated syspref stuff

This patch adds the syspref requirements for unmediated ILL requests. It
is a recreation of
https://bugs.koha-community.org/bugzilla3/attachment.cgi?id=66628&action=diff
which had diverged sufficiently as to make it impossible to apply.

* installer/data/mysql/atomicupdate/illunmediated_tables.sql: New
  file.
* installer/data/mysql/sysprefs.sql: Add `ILLModuleUnmediated`.
* koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/admin.pref:
    Add `ILLModuleUnmediated` handling.

Signed-off-by: Stephen Graham <s.graham4@herts.ac.uk>
Signed-off-by: David Peacock <d.m.peacock@herts.ac.uk>
Signed-off-by: Jayne Maisey <j.maisey@herts.ac.uk>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>