Add parent::run() call
Only set tcpdf renderer when pdf is requested
Do not confirm is confirm message is falsy
Invoke renderDataCellContent correctly

Because renderDataCellContent is protected, it cannot be called from a
non-Column derived class. So create a small wrapper that invokes the
function for us.

Also, invoke the function when value is defined, as the user might have
overriden the attribute value
Merge branch 'workaround-datacolumn-protected'
Make _triggerDownload protected
Add onRenderSheet event

To apply final sheet modifications
Merge branch 'on-render-sheet'
Use getDataCellValue for DataColumns
Merge branch 'use-getvalue'

Conflicts:
	ExportData.php