Bug 35413: Terminology: Manage issues (issue_manage)

Bug 35413: Terminology: Manage issues (issue_manage)

This patch updates several files which use the term "issues" without
context, changing them to "Vendor issues." Unchanged is the vendor
issues page template, vendor_issues.tt, which is updated in Bug 35417.

To test, apply the patch and go to Acquisitions.

- Search for a vendor and view the details.
- You should see a "Vendor issues" link in the sidebar.
- Go to Patrons and search for a patron. View the patron's details.
- Click More -> Set permissions.
- Under Acquisitions management you should see "Manage vendor issues
  (issue_manage)"

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>