LPS-32192 Change asset selection type in Asset Publisher to a radio 

This is before:
![Screenshot_15_01_13_10_13](https://f.cloud.github.com/assets/203395/67336/656f8428-5efa-11e2-84e1-9bc00bb143c4.png)

And this is after:
![Screenshot_15_01_13_10_35](https://f.cloud.github.com/assets/203395/67337/6ab46aa2-5efa-11e2-87a6-e9aaeaf79bf2.png)