Bug 24837: Rename selectbranchprinter.pl to set-library.pl

Bug 24837: Rename selectbranchprinter.pl to set-library.pl

This renames the selectbranchprinter.pl file to the more
fitting set-library.pl.

To test:
- Change the library with "Set library" from
  - The menu in the top navigation bar
  - The circulation start page
- Verify the help link on page leads to the correct
  section in the manual
- Read the code... and verify all occurences have been caught

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>