Bug 8007: Discharge management

Bug 8007: Discharge management

This patch is the main patch. It adds new package and files for the new
pages (opac-discharge, members/discharge and members/discharges).

At the intranet, it is now possible to generate a discharge for a patron.
At the opac, a patron can request a discharge and a discharge if it has
been validated by a librarian.

Requirements:
    The perl module PDF::FromHTML

New sysprefs:
 - useDischarge: Allows librarians to discharge borrowers and borrowers
   to request a discharge

New letter with a letter_code DISCHARGE.

Test plan:
- Switch on the syspref useDischarge.
- Verify a new tab appears in the patron page (intranet and opac).
- Verify the discharge cannot be generated if the patron has issues.
- Verify the patron can request a discharge from it's opac area.
- The request appears on the main page (intranet).
- Generate the discharge from the intranet.
- Try to download it (from the opac and the intranet).

Signed-off-by: Lucie <lucie.rousseaux@dracenie.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>