pad_impexp: Use jQuery to build the import failure popup
pad_impexp: Use jQuery to build the import failure popup

This reduces the chances of accidentally introducing an XSS
vulnerability.

storytouch/etherpad-lite,ether/etherpad-lite,ether/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,storytouch/etherpad-lite