Print buttons

[coudot]

Need to see if we need the print and export buttons.

After migration of DataTables, a new syntax is needed to enable them.

[coudot]

The current stable version has this buttons:

We just need to use the new Datatable options, like https://datatables.net/extensions/buttons/built-in#Print

We may need to review how we call Datatable and follow upgrade notes: https://datatables.net/upgrade/index#Major-releases

For information, we used DataTables 1.10.16 in Service Desk 0.5, and we now use 2.0.8 for Service Desk 0.6.

[coudot]

I restored print buttons in #183

CSV or PDF export is available in datatables, but only relies on displayed data (which can be truncated). We need to think about it if we want to add an export feature.