Adds a 'New Subscription' option for selection from the detail page of a record.

Adds a 'New Subscription' option for selection from the detail page of a record.

NOTE TO DOCUMENTATION WRITERS: Due to the limitations in the serials module search
interface, some users may find it easier to use the standard catalog search to locate
an item on which to create a subscription record, and then use this new button to
create a subscription from the detail page.

Signed-off-by: Daniel Sweeney <daniel.sweeney@liblime.com>
Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>