The DIV generated by the top level component error handler should have a class

In order easily style the top level component error handler back stop it should have a class (like ''hyperstack-top-level-error-boundry' that you can set the CSS for.

I.e. make the text smaller, and give it a white background, etc.

Here is a patch:

```ruby
module Hyperstack
class Hotloader
module AddErrorBoundry
# don't attempt the alias unless the method is defined.
# for example if HotLoader is not included in the stack
alias original_display_error display_error if method_defined? :display_error
def display_error(*args)
DIV(class: 'hyperstack-top-level-error-boundry') { original_display_error(*args) }
end
end
end
end
```

**Be sure to have the method_defined? guard defined, otherwise you may discover in test or worse in production things won't boot**