Remove Makefile, document how to use pipenv

[nirs]

The recently added Makefile is not useful:

• rose-client and rose-admin need arguments, running them using the makefile is not a good idea
• this won't work on platforms where installing make is hard
• running "pytest" is nicer and more useful then "make test" best use the simpler and powerful way instead of having tow ways to run the tests.

We need to remove it and document instead of to use pipenv, replacing the old way using bare pip.

Playing with pipenv, it seems that the best way to use it is:

Requirement:

• pip install --user pipenv

Setup for users:

• pipenv install

Creating a shell for running the server or client:
pipenv shell

Setup for developers:

• pipenv install --dev

With this the rest of the documentation does not need any change.

It is possible to use "pipenv run" but having to repeat this is annoying and error prone, I don't want to make it harder for teachers or students.

Notes:

• Setup for developers should be separate from user setup, we don't want to confuse users with developers tasks.
• For users we have two use cases:
  • students - need to run both local server and one or more clients for testing their code
  • teacher - need to run the server, and ask student to connect to the server
    Maybe we need to document this separately to make it easier?
• Students are young and may have no technical experience, we need to avoid stuff like "old fashioned way" since they don't know anything about it

[nirs]

@rollandf can you review this?