Bug 23078: Use Koha.Preference in OPAC global header include

Bug 23078: Use Koha.Preference in OPAC global header include

This patch updates the OPAC's doc-head-close.inc so that it uses
'Koha.Preference' syntax to output system preference data. The patch
removes handling of two preferences from Auth.pm which which are covered
by this template change.

This patch also makes some minor changes to consolidate multiple
template checks for "bidi"

To test, apply the patch and test the affected OPAC system preferences:

 - OpacFavicon
 - opaclayoutstylesheet
 - OPACUserCSS
 - OPACBaseURL

Confirm that changes made to these preferences are reflected in the
OPAC.

Signed-off-by: frederik <frederik@inlibro.com>
Signed-off-by: Nadine Pierre <nadine.pierre@inLibro.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>