Duplicate attribute names

Duplicate attribute names shouldn't be possible

![image](https://user-images.githubusercontent.com/54511302/78361485-c2bfbf80-75b8-11ea-8607-59742eff8eb2.png)

Same goes for domain object names

![image](https://user-images.githubusercontent.com/54511302/78361629-00244d00-75b9-11ea-9447-b37f074b34e8.png)



