Make the Workspace Manager sexier (#353)

Now the folder combo box is a WideComboBox with a fixed width of 230px, which should fix the
problem described in #353.

Translations have been added.

Screenshots:
![newwsmanager](https://f.cloud.github.com/assets/2470768/1008644/c09a081e-0b2a-11e3-91e3-2297abf9fdff.png)
![newwsmanageropened](https://f.cloud.github.com/assets/2470768/1008645/c33ac720-0b2a-11e3-817a-86ab73383d53.png)
![newwsmanagerfr](https://f.cloud.github.com/assets/2470768/1008717/99153fbe-0b2c-11e3-9357-850ea5c583b2.png)