sets a new label for a cell in the footer
| col | number | the index of a column |
| label | string | a new label for the specified footer's column. Can contain img:[imageUrl]Text Label |
| ind | number | the index of a footer row (optional, 1 by default) |
//set a new label for the first cell in the first footer's line
mygrid.setFooterLabel(0,'New Label');
//set a new label with an image for the first cell in the second footer's line
mygrid.setFooterLabel(0,'img:[../codebase/imgs/image.gif]New Label',1);