Bug 18811: Change visibility checks in authorities.pl

Bug 18811: Change visibility checks in authorities.pl

The check is now <=-4 or >=5, but the framework uses 0 for Show all and
-5 for Hide all. (Note that sql installer scripts also use 8.)
When modifying an authority, the script also showed hidden fields when
filled, since it did not check the hidden field but only the tab field.

NOTE: The proposed solution restores consistency, but will remove hidden
fields from the MARC record.

Test plan:
[1] Set field 942a to Show all in an authority framework.
[2] Open a new record in this framework and verify that you see 942a.
[3] Edit an existing record in this framework and verify again.
[4] Set field 942a now to Hide all in this framework.
[5] Open a new record in this framework and verify that 942a is hidden.
[6] Edit an existing record in this framework and verify again.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>