Proposed Changes so that Grid with BeanItemContainer will populate Excel Rows

[cscumming-dwss]

made changes to ExportToExcelUtility.addGenericRow for Issues #3 and possibly #10

However, one caveat: in my application I extended Grid with two convenience methods, which could possibly be included in the Utility

`
public Object[] getVisibleColumns() {
List visCols = new ArrayList();

    for (Grid.Column gcolumn : this.getColumns()) {
    	if (!gcolumn.isHidden()) {
    		visCols.add(gcolumn);
    	}
    }
	return visCols.toArray();
}

public String[] getHeaderColumns() {
	List<String> visCols = new ArrayList<String>();

	//Remove hidden columns
    for (Grid.Column gcolumn : this.getColumns()) {
    	if (!gcolumn.isHidden()) {
    		visCols.add(gcolumn.getHeaderCaption());
    	}
    }
	return visCols.toArray(new String[0]);
}

`

[cscumming-dwss]

I'm withdrawing the pull request - my code is out of date - @brunojcm code seems address the issue