Bug 24156: move ColumnsSettings to TablesSettings

Bug 24156: move ColumnsSettings to TablesSettings

We are preparing the ground with this patch. As the "Columns settings"
page will now add the ability to modify settings for the whole table, it
makes sense to rename the file and the variables.

Note that the controller script (admin/columns_settings.pl) and the yml
(admin/columns_settings.yml) files have not been moved to not break
shortcuts and abits people could have. But if QA decides, it could be
easy to do.

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>