Change user's nickname to username

[QubitPi]

Make this a standalone PR. Even 1 line of change is still a valid PR

    @Query("CREATE (u:User { oidcid: $oidcid, nick_name: $nickName }) RETURN u")
    User createUser(@Param("oidcid") String oidcid,
                    @Param("nickName") String nickName);

What's the rationale of nickname instead of the standard username/display_name where all other application use?

P.S. In English, everyone has a name, but not everyone has nick name because some consider a nick name impolite