Bug 31671: Add print slip button to transfer page

Bug 31671: Add print slip button to transfer page

This patch reimplements/rebases Lucas' patch and adds a style
modification to the button.

To test:
1. Apply patch
2. Go to Circulation / Transfer
3. Try transfering some items and notice the 'Print slip'
   button
4. Try clicking on it and make sure it generates correctly and with the
   correct information on the slip

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>