RFP Create reviews

Added reviews controllers, model and views. Don't merge until episode is done.
I'm still not sure. I think the code that you changed it to should do the same thing. My guess is that maybe you had some users where the `avatar_url` is not `nil` but is instead an empty string.

Either way, you could clean this up a little bit if rewritten as:

```ruby
url = user.avatar_url? ? user.avatar_url : 'MrG.png'
```