Row decorators with conditions

[rodrigo-martinez]

The renderer of rows is not validating the conditions before calling the decorator. As in the rendered of Cells, an if is needed who ask for the validConditions before calling the decorator.

Beside this, when added a ClassDecorator with conditions, the decorator adds the new class to the class attribute of row, so after that the class is added for every next rows. I don't know the best way to fix this, in the code, I added at the begining of the foreach an assigment to reset the class value.

[rodrigo-martinez]

I found the addVarClass that is cleaned after each row rendered. So changing de ClassDecorator instead of using de addClass use the addVarClass

[fzipi]

This change seems useful, could it be merged?