Mg nav third level menu

![image](https://cloud.githubusercontent.com/assets/2095625/3287152/eb5da722-f553-11e3-99c0-01a29188af91.png)

![image](https://cloud.githubusercontent.com/assets/2095625/3287161/128cc742-f554-11e3-8d46-7ae4eceeeba2.png)

Yeah that one is tricky. I'll leave it for now though. I don't think adding more classes to the markup is a good idea and the Scss is pretty intricate there, but if you find a better refactoring of it, that would be nice!