DUI: hover highlighting for nested classes.

Have the same hightlight behaviour in the green box - same color as classes / methods
![image](https://cloud.githubusercontent.com/assets/8158404/4978760/28dd9596-68f2-11e4-8d9e-2ad860e04b30.png)

Reviewers
@Benglin ,@vmoyseenko, please take a look.
Link to YouTrack:
[MAGN-5359](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5359) DUI: Make hover for namespaces