Message if perfectly distributed

[llrs]

If there is one sample per batch with a given condition, message the user that the experiment is perfectly randomized.
(No need for warn: This is a good thing :)

[llrs]

This might be complicated as this could only be done if there is one condition (which might be the result of combining multiple conditions), in this case it doesn't make sense to use the package...

[llrs]

If multiple conditions resulted in one perfectly distributed we could do that...
In fact we could simply use index4index to do the splitting in that case.