Bug 12062: Follow up to fix more untraslatable cases

Bug 12062: Follow up to fix more untraslatable cases

This patch modifies staff printslip.tt to take into account
caller. Also fixes similar problem on opac printslip.tt

To test:
staff
1. Print hold transfer slip
2. Print transfer slip
3. Print member slip
opac
4. Print self checkout slip

5. Update translation files, check new strings are present

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>