Fix margin bottom on Large Curated List Tile

In order for masonry.js to correctly calculate the height of this tile, the "mb" class needs to be on the same div tag as "masonry_item" so I am removing "mb" from the div with "grid" and putting it on the "masonry_item".
Merge pull request #202 from CruGlobal/large-curated-list-tile2

Fix margin bottom on Large Curated List Tile