option added to display tabs vertical on the left side

Added an option to display the tabs vertical on the left side:
![vertical option](https://cloud.githubusercontent.com/assets/4180675/4404037/33b9ff14-44ac-11e4-90b3-476c0832edfb.png)

![bildschirmfoto 2014-09-25 um 14 00 28](https://cloud.githubusercontent.com/assets/4180675/4404040/3b464fee-44ac-11e4-9de7-b8c8ad51ce8d.png)