Bug 19036: Add ability to auto generate a number for account credits

Bug 19036: Add ability to auto generate a number for account credits

In some areas it's required to sequentially number payment slips /
receipts.

This patch adds a database column accountlines.credit_number and a
system preference AutoCreditNumber to control how this number will be
generated.  The following options are available:

- Do not automatically generate credit numbers.
  This is the current behaviour and the default syspref value.

- Automatically generate credit numbers in the form <year>-0001 (annual)

- Automatically generate credit numbers in the form
  <branchcode>yyyymm0001 (branchyyyymmincr)
  where <branchcode> is the branch where the user (staff member) is
  logged in

- Automatically generate credit numbers in the form 1, 2, 3
  (incremental)

It also adds a column (hidden by default) in the table under
Transactions tab to display this number.

Test plan:
0. Apply patch, run updatedatabase and update_dbix_class_files
1. Go to Admin » Column settings, and uncheck the 'hidden' box for
   column credit_number in table account-fines. It will be easier for
   testing
2. Create a manual credit for a borrower. Verify in Transactions tab
   that this credit has no number generated
3. Change syspref 'AutoCreditNumber' to 'incremental'
4. Create more manual credits, and verify that the numbers generated are
   1, 2, 3, ...
5. Change syspref 'AutoCreditNumber' to 'annual'
6. Create more manual credits, and verify that the numbers generated are
   '2020-0001', '2020-0002', ...
7. Change syspref to 'AutoCreditNumber' to 'branchyyyymmincr'
8. Create more manual credits, and verify that the numbers generated are
   'BRANCHA2020020001', 'BRANCHA2020020002', ... (assuming you are
   connected to library BRANCHA, and it's February 2020)
9. Set library to another one, say BRANCHB
10. Create more manual credits, and verify that the numbers generated are
    'BRANCHB2020020001', 'BRANCHB2020020002', ...
11. Edit the letter ACCOUNT_CREDIT, and add [% account.credit_number %]
    somewhere. Go back to Transactions tab and click on 'Print' for one
    line that has a credit number. Make sure the number is there.
12. prove t/db_dependent/Koha/Account.t

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>