Support variable height cells in .multi-list

Not sure if the would be a suitable inclusion. This modification allows the `.multi-list` to have variable height cells. Cannot make it work for `.matrix` due to the borders though. As per the new grid system it does also require the empty comments between elements.

Old style — http://jsfiddle.net/Y2zrU/24/
New style — http://jsfiddle.net/Y2zrU/29/