Fix for Bug 6957, authors disappearing when emailing lists

Fix for Bug 6957, authors disappearing when emailing lists

Standard author information wasn't even in the template markup, only
"additional author." Added standard author and improved output of
additional authors (hiding label when empty).

Also added subtitle via GetRecordValue (see bug 3550).

Also added check for and output of OPACBaseURL in order
to make OPAC links in the email clickable.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
QA revision:  renamed OPACBaseurl to OPACBaseURL for consistency

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>