Allow overriding the wrapper class

[donv]

The wrapper now has a mb-3 class by default which is correct by the Bootstrap 5 migration guide and documentation. 👍

However, when you want to remove the bottom margin like some of the tests do, there should be a way to omit the mb-3 class. I think wrapper_class: false should do this, so I'll add it to this PR.

Then, when you add classes, you should be able to add them to a clean slate. That means that you need to include the mb-3 class if you want it.

What do you think?

[lcreid]

Thanks for submitting this PR. I agree that we should have some way of overriding the default behaviour. Take a look at my comment and let me know what you think.