Add some simple styling to the .parent-link

Add some simple styling to the `.parent-link` that is generated when you are looking at a drop down menu in mobile state.
I use the $topbar-link-weight that by default is set to `bold`. 

This is especially handy when you generate your topbar and can't add label's to your submenu's:
![image](https://f.cloud.github.com/assets/2445415/706227/913a0f0c-dde8-11e2-8e5d-fcac7b742288.png)