Bug 14973: Check existing biblio when submitting a purchase suggestion (opac side)

Bug 14973: Check existing biblio when submitting a purchase suggestion (opac side)

Test plan:
- Go to opac suggestions page (opac-suggestions.pl) and click on "New purchase suggestion",
- type the title (and author?) of a document that stand in you database
- you should get a warning message about an exiting biblio.
- clicking on confirm your suggestion add it, cancel does nothing

Signed-off-by: Nicole Engard <nengard@bywatersolutions.com>
Signed-off-by: Lisette Scheer <lisetteslatah@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>