Bug 10115 - Hiding advanced search in Orders search tab removes plus button

Bug 10115 - Hiding advanced search in Orders search tab removes plus button

The logic of the JavaScript for showing and hiding additional options in
the orders search form wasn't quite right, resulting in the +/- control
being hidden incorrectly.

This patch corrects and simplifies the JS in order to fix the problem.

To test:
 - Open any page in Acquisitions which shows the orders search
   form in the header search bar (for instance, Acquisitions home).
 - Open the orders search tab and click on the "+" to show more
   options.
 - Click the "-" to hide the additional options. The additional options
   should now be hidden and the "+" displayed.

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Works as expected
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>