Display error message on AJAX errors
Display error message on AJAX errors

This display the `errorLoading` translation when there is an error
during the AJAX cycle. Previously we were just throwing these errors
out, now we are actually displaying an error message.

This closes https://github.com/select2/select2/issues/3501

murb/select2,fk/select2,bottomline/select2,ZaArsProgger/select2,megahallon/select2,inway/select2,iestruch/select2,murb/select2,stretch4x4/select2,michael-brade/select2,select2/select2,iestruch/select2,inway/select2,ZaArsProgger/select2,select2/select2,michael-brade/select2,stretch4x4/select2,megahallon/select2,NabiKAZ/select2,NabiKAZ/select2,bottomline/select2,fk/select2