python36 replaces python27 and will be the standard interpreter

Since the beginning of 2020, python2 is declared end of life. Therefore, the platform-provided python27 interpreter will be removed in the near future and we will not be able to offer support for python27.

The default python interpreter will become python36 which is already provided. Python35 will remain available on the Virtual Machines and the Hadoop cluster.

For the notebooks service, we will only keep python36.