Small changes to the new API needed

• rename kmeans_trainer parameter in GMMMachine to kmeans_machine
• make the Kmeans and GMM machines available in bob.learn.em.
• [ ] The __call__ methods are missing.
• load methods are missing
• setup.py requirements.txt and meta.yaml is not updated.

Some other things that I will add to this issue. The changes don't need to be addressed now.