Bug 8764 - Template change "Authors" to "Additional authors" in OPAC

Bug 8764 - Template change "Authors" to "Additional authors" in OPAC

This patch simply changes "Authors" to "Additional authors" in the OPAC. This label describes authors that are added via the MARC 700 fields, which are added or additional authors.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Works as advertised, and seems to make sense. Only affects the display
when XSLT is not enabled.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>