Bug 3388: Restore account number on vendor page

Bug 3388: Restore account number on vendor page

This patch makes it possible to add the account number to the
vendor information. The used field aqbookseller.accountnumber was
already existent in the database.

To test:
1) Add a new vendor with accountnumber
> Verify form has a field for accountnumber
> Verify accountnumber does show up on vendor summary page
2) Edit this vendor, change accountnumber
> Verify change was correctly saved and new number is displayed on
vendor summary page
3) Delete accountnumber

Signed-off-by: Liz Rea <lrea@nekls.org>
Tested 1-3, no troubles found.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>