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 
@joneslee85 I'm for the assertion style in this case. `BasicObject` is an exceptional Ruby class. Having Minitest to fiddle with injected methods may introduce bugs in the future. A direct invokation of `#respond_to?` is safer. :)