Improvement; Changed short-object-description view so it displays an image preview if the provider name is sonata.media.provider.image

Before:
![screen shot 2014-02-03 at 13 07 18](https://f.cloud.github.com/assets/3961971/2064414/c976a3ca-8ccb-11e3-9d80-c6dfa2fe3418.png)

After: 
![screen shot 2014-02-03 at 13 05 21](https://f.cloud.github.com/assets/3961971/2064405/8b36a8d0-8ccb-11e3-8645-08b82854b131.png)