Issue with table lookup

[petrovskyy]

In case table is rendered later than directive initialisation ctrl.tableElement gonna be empty.

I would suggest moving table element lookup

if(elementScope.ctrl.tableSelector) {
   ctrl.tableElement = $document.find(elementScope.ctrl.tableSelector);
}
 

into function exportTable() or click handler

[Epotignano]

Could you create a PR without problem!