Added the row <div> to every panel-grid for consistency

The row style is a great feature, however, I think it would be much better for developers and end-users alike to have more consistent markup in place. Currently the div with a class of panel-row-style is only outputted if a style is selected.

For example, from a developers point of view it would be a pain to create rows that stretch from left to right (width:100%;) and have to contents (panel-grid-cells) centered if no row-divs is available. For the end user this could turn out equally annoying if a developer failed to account for the "default" style properly, or the if the default style is very different from other row styles. 

At the very least, there should be a filter or a settings option to give developers or users the option to include a panel-row-style-default div. What do you think? Thanks