Fallback solution when the user already has anaconda installed

[zerothi]

This problem has now occurred several times:

The problem occurs when the user has a pre-installed Anaconda. We have seen at least 3-4 cases of this now.

1. It happens because the Anaconda distribution was used.
2. When that is pre-installed then any conda-init will not overwrite the old settings because it is the conda from the old installation that is referenced
3. Conda installing packages won't work either because there are so many base packages installed in the base environment that nothing will ever be installed.

I think the simplest solution in this case would be to:

1. disable the anaconda installation,
2. Ensure that the conda init we issue is from the newly installed one
3. Double check that in a new terminal, I guess this can be done in the auto-script, not so much in the manual installation guide.
4. Potentially we should have a good description of how to delete old installations

I am not too fond of executing un-install scripts on studenst pc's at the moment. Lets try and solve this by information, and guides for handling this so we can actually learn a bit from this experience.

@philipnickel tagging you, we should discuss this tomorrow ;)

[philipnickel]

• On Windows: Link to uninstall guide and ask to run script again. (Needs merge of pull request on uninstall guide on pythonsupport-page)

• On Mac: Prompt user for deleting Anaconda-installation. Otherwise exit script with descriptive error-message