updates the starting position for paged navigation and then rebuilds the graph based on the selected page
function(direction, cloud_element) {
  var start = $( '#cloudGraphPagingStart' ).val();
  var rows = $( '#cloudGraphPagingRows' ).val();
  var startAt = start ? parseInt(start) : 0;
  var numRows = rows ? parseInt(rows) : 20;
  var newStart = Math.max(startAt + (rows * direction),0); 
  $( '#cloudGraphPagingStart' ).val(newStart);
  
  var graph_element = $( '#graph-content', cloud_element );
  $( '#canvas', graph_element).empty();
  init_graph( graph_element );  
}