Bug 10065 - Style invoice edit form according to standard structure

Bug 10065 - Style invoice edit form according to standard structure

The structure of the invoice edit form does not match that of similar
forms in the staff client. This patch alters it to be consistent.

To test you must also have the patch for Bug 10046 applied.

Go to Acquisitions -> Invoices and search for invoices. Click an invoice
to view/edit details. The form displaying fields for shipment date,
billing date, etc. should look correct and work correctly.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>