Bug 14247: Add system preference for news display

Bug 14247: Add system preference for news display

Test plan:

* Apply dependant patch 14246 (if not done already).
* Apply current patch.
* Log into the Staff client, go to 'Administration' -> 'Global Preferences' -> 'Tools', a new section titled 'News' should appear with a single option named 'NewsAuthorDisplay'. Available values should be 'Not at all', 'OPAC only', 'Staff client only' and 'Both OPAC and staff client'. By default the value should be 'Not at all' (to mimic existing behaviour, important!).
* Change the value to something different and save the changes.
* Use the mysql command line client to connect to the Koha database:
  $ mysql -u kohaadmin -p -D koha
* Enter the following query:
  SELECT * FROM systempreferences WHERE variable = 'NewsAuthorDisplay';
* Check to make sure that the 'value' column has changed to reflect the choice you made in the above step.

Separate SQL testing (clean installation of Koha):
* Koha$ mysql -u root < create_koha_test_db.sql
* Koha$ mysql -u koha_test -D koha_test < installer/data/mysql/kohastructure.sql
* Koha$ mysql -u koha_test -D koha_test < installer/data/mysql/sysprefs.sql

Testing the update script works the same way:
* Koha$ echo "DELETE FROM systempreferences WHERE variable = 'NewsAuthorDisplay';" | mysql -u koha_test -D koha_test
* Koha$ mysql -u koha_test -D koha_test < installer/data/mysql/atomicupdate/add_news_prefs.sql

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>