Unique DAG Operator names

Fixes [MLHR-1382](https://malhar.atlassian.net/browse/MLHR-1382)

![image](https://cloud.githubusercontent.com/assets/1390651/4170116/07001f30-352f-11e4-8f16-044f44050b45.png)
![image](https://cloud.githubusercontent.com/assets/1390651/4170122/176f62fe-352f-11e4-9afb-ebb2aa21ab81.png)