change experimental module to models

[huiwengoh]

Changing function import namespace from experimental to models following migration in https://github.com/cleanlab/cleanlab/pull/601

[jwmueller]

one change though that should be made temporarily is:

In the requirements.txt for each of these updated examples, state that this example requires the developer version of cleanlab from github

# This notebook currently requires the latest developer version of cleanlab: pip install git+https://github.com/cleanlab/cleanlab.git

Cf. https://github.com/cleanlab/examples/blob/master/active_learning_multiannotator/requirements.txt