Bug 17346: Make checkin column hidable

Bug 17346: Make checkin column hidable

To test:
1) Go to columns_settings.pl --> Circulation --> issues-table and note that you cannot change the settings for checkin.
2) Go to columns_settings.pl --> Patrons --> issues-table and note that you cannot change the settings for checkin.
3) Apply the patch.
4) Go to both tables again and note that you can now change the settings.

Followed test plan, works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>