Added methods for redirect paths similar to what devise do to allow modules

I was using this gem in a module but it would error out since every redirect is hard coded to root_path.

I changed this to allow users to override the paths within their own controller like so:

```ruby
class MyCustomModule::DeviseAuthyController < Devise::DeviseAuthyController

  protected
    def after_authy_enabled_path_for(resource)
      my_own_path
    end

    def after_authy_verified_path_for(resource)
      my_own_path
    end

    def invalid_resource_path
      my_own_path
    end
end
```