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 
Do we have a bug for having a normalized role name (see the code above that does `r.Name.ToUpper() == roleName.ToUpper()`?