Restrict use of the server Python code env and default code environment for users/groups

Two issues I would like to see addressed. First I would like to be able to restrict the use of the server Python code env. We don't use this code environment and a lot of our users get confused when running recipes and Jupyter Notebooks as they install a Python package in their allocated Python code environment but they get errors importing the package since they incorrectly selected the server Python code environment since it's the default. While it is possible to set the code environment on projects this has to be done per project and otu have to remember to do it. 

The second request is to be able to set default Python code environments per user or per group. This will allow us to basically allocate generic code environments in advance to users and prevent the issue of them incorrectly leaving the server default code environment.