Bug 29530: Fix handling of NumSavedReports preference in reports table

Bug 29530: Fix handling of NumSavedReports preference in reports table

This patch updates the way the NumSavedReports preference value is used
on the saved reports page so that the setting is correctly incorporated
into the DataTable.

The patch also expands the description of the NumSavedReports preference
in order to clarify the expected behavior when no value is saved.

To test, apply the patch and go to Administration -> System
preferences and note the value of NumSavedReports.

 - Go to Reports -> Use saved.
 - Confirm that the first page of saved reports shows the number
   specified in NumSavedReports.
 - In the "Show" dropdown menu, confirm that the number from
   NumSavedReports is preselected by default.
   - Expand the dropdown menu to confirm that the NumSavedReports number
     is positioned sequentially with the default values. For example, if
     NumSavedReports = "78," the menu options should be
     "10, 20, 50, 78, 100, All".
 - Test with various values of NumSavedReports. A blank value should
   result in the "All" option being selected. A non-numeric or
   non-positive value should result in the default set of options being
   used ("10, 20, 50, 100, All").

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>