Feature/SK-1688 | Rework Client

[carl-andersson]

• Implementation of a python client which imports implementation rather than dispatches the implementations.
• Changes how environments are handled so that they primarily extends the calling environment rather than completly replacing it
• The client restarts itself with the correct enviroment
• An example of the new implementation is in examples/importer-client
• The old client still works

Missing

• Needs testing, especially windows
• fedn run train / validate / test will not work