Bug 23612: If no columns in a table can be toggled, don't show columns button

Bug 23612: If no columns in a table can be toggled, don't show columns button

This patch makes a change to the JavaScript setup for DataTables button
controls so that if there are no toggle-able buttons (or there is no
columns configuration at all) the column selection menu button will not
appear.

To test, apply the patch and go to Administration -> Columns settings.

 - In the Administration section, find the section for the "libraries"
   table.
 - In the "Cannot be toggled" column, check all the checkboxes.
 - Save.
 - Go to Administration -> Libraries.
 - At the top of the table there should be no "Columns" button, only
   "Clear filter" and "Export" buttons.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>