Implement Scope#class, Scope#inspect, LayoutScope#class and LayoutScope#

Not sure if this is the desired implementation of these methods, but it should be a starting point for enhancment and discussion.

cc @joneslee85, @jodosha 
The formatter of the string is wrong: the `#` comes as first character before the `<`.

```ruby
[1] pry(main)> class Book
[1] pry(main)* end
=> nil
[2] pry(main)> Book.new
=> #<Book:0x007ffaed798f70>
```