[Sprint #6] User Account Page & its test code

---- NOTE ----
1. User Account Page Feature is added
2. User Account View code is added
3. urls & simple template page for account is added
4. Test code for AccountView is added
so, if we maintain `DetailView` ( i agree with your idea that this is more explicit way. ), how about to change `get_object` implementation.

```
def get_object(self):
    return self.request.user
```

in this case, we can access user via session directly.