add users editable support

[``* `#17014` users editable``](http://community.openproject.org/work_packages/17014)
@ulferts @hschink @myabc I agree, I was under the wrong opinion that this layout is going to change (where in reality it was already the new layout). As a solution I propose to add a .renderStrategy to the propertyData with a format like 
```
{type: 'select', 'name': 'status.name', 'placeholder': '-', 'embedded': false}
```
or something similar (maybe we don't need the embedded part since we can check for a dot in the name)