solve issue #860: implement language toolbar

Addresses #860. Adds a toolbar in all pages. Switches automatically to the chosen language once it has been selected.

Initially in German:
![2013-12-04-103929_1366x768_scrot](https://f.cloud.github.com/assets/191955/1676063/c4d8a40e-5d13-11e3-842e-f28108666694.png)

Switch automatically to English:
![2013-12-04-103936_1366x768_scrot](https://f.cloud.github.com/assets/191955/1676066/c996e410-5d13-11e3-8488-dd47b576f45c.png)