Use a grid without margin in the content area.

There is a problem with the layout (extra margin) if the grid is used in the content area.

I've removed the margins if the grid is in the `#column-content`.

![bildschirmfoto 2013-11-25 um 10 49 04](https://f.cloud.github.com/assets/157533/1611844/477d96ee-55b7-11e3-9d7e-ec5f381704ab.png)

![bildschirmfoto 2013-11-25 um 10 48 47](https://f.cloud.github.com/assets/157533/1611843/47664b1a-55b7-11e3-88c9-55b5a2d59033.png)

@href please take a look
fixes #41