Add a buildtask for cleaning up snapshot directories

Due to the amount of time this fails, it seems prudent to have a task ready for cleaning up.
Obviously, this isn't the most robust implementation, but it has a dry run and is useful for administrators/operators who are trying to free disk space.
This could be run in CLI, so your html won't make sense.

Do you think it's better for the task to run in live mode and opt-out instead of opting in?