function findColumn(model, index){
      var column = null;
      for (var i=0; i<model.rows.length; i++){
        var r = model.rows[i];
        for (var j=0; j<r.columns.length; j++){
          var c = r.columns[j];
          if (dashboard.idEquals(c.cid, index)){
            column = c;
            break;
          } else if (c.rows){
            column = findColumn(c, index);
          }
        }
        if (column){
          break;
        }
      }
      return column;
    }
finds a column by its id in the model