Activities: Activity Enrolment Summary report ooification

[SKuipers]

This PR sets up the functionality for DataTables used on report pages, enabling them to be displayed as an HTML table as well as easily printed and exported.

The ooified logic uses a format url parameter to determine the type of data table to render. In the future when we implement routing this parameter can be part of the controller request-response handling to automatically apply the right template and headers based on the content type.

• OOifies the Activity Enrolment Summary as an example.
• Adds a PrintableRenderer for the DataTable, which displays a title with the table and strips out any Action/Expandable columns.
• Adds row-highlighting logic to the SpreadsheetRenderer class.
• Creates an export.php front-controller for pages that require no HTML headers/output.
• Adds some print css styles, particularly to prevent page breaks inside a table row.