Add enrollment preprocessing CLI tool

[Kakadus]

fix #1490

Upload my progress on the cli tool from monday.

• There needs to be a link to the user export route somewhere.
• There is probably a test missing for the cli tool.
• The django-pylint plugin has a problem with linting the preprocessor (I manually linted it though)
• codecov does not see the tools

[richardebeling]

Looking good! :)

[richardebeling]

More in-depth this time, so a few more comments, but it's all very detail-y.

[Kakadus]

I were ably to combine initial excel parsing and conflict grouping, because of direct conversion from Cells to Users, but the update logic needed more complexity (Codacy is not very happy)

[janno42]

As discussed: The tool asks for the same user multiple times.

[janno42]

Seems to work now

[Kakadus]

Just to be sure: Currently the whole userdata from the conflict is shown, so this question is possible:

First_name
---------
existing: 'Bastius' (Bastius Prorsus, same@email.com)
imported: 'Lucilia' (Lucilia Manilium, same@email.com)

Selecting imported only applies the conflicting field, here the first name (resulting data: Lucilia Prorsus, same@email.com)
Of cause, you are then asked about Prorsus vs Manilium later.
Instead, we could show the resulting data always, so

existing: 'Bastius' (Bastius Prorsus, same@email.com)
imported: 'Lucilia' (Lucilia Prorsus, same@email.com)

is asked instead.

[janno42]

We can leave that as it is now. I'd say the second way makes interpretation harder.