Changed top bar styles to fix alignment issues

This is to fix the text alignment issues in the current top bar version. I have changed it to use line-heights rather than paddings to centre the text. also removed the negative margins used on the arrows in the dropdowns so that they use the line-height as the text. 


![Topbar-problem](https://f.cloud.github.com/assets/435107/370757/0b15e878-a301-11e2-9f4e-e533502e4e5f.png)
![Topbar problem responsive](https://f.cloud.github.com/assets/435107/370758/0b431410-a301-11e2-9b89-5a0154b13b7e.png)