Bug 14280: Add branches fields to discharges letters

Bug 14280: Add branches fields to discharges letters

Currently, when generating a discharge letter, branches fields are not translated in the letter (<<branches.branchname>>, <<branches.branchaddress1>>, etc.)
This patch fixes that.

How I tested:
- Set syspref 'useDischarge' to 'allow'
- Go to Home > Tools > Notices & Slips
- Edit DISCHARGE, add to 'Email message':
<p><<branches.branchname>><br />
<<branches.branchaddress1>><br />
<<branches.branchaddress2>><br />
<<branches.branchaddress3>><br />
<<branches.zip>> <<branches.city>><br />
</p>
- Go to detail page of a patron > discharge
- Click 'Generate discharge'
- Verify that the PDF contains the information above.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>