Stop using navigation properties in UserStore

- Will follow up in a different PR with fixup/loading of navigation properties (they are not populated correctly today)
- Also adds some tests that load from the database (confirming that navigation properties aren't loaded today)

cc @suhasj @divega 
Similar to the change before this one... is the object graph correctly fixed up by just removing the userRole? If yes, why comment this code instead of removing it? If no, what do you propose we use instead of the navigation property?