update ariadne mapping

[fschreyer]

Purpose of this PR

Some updates of the ariadne project mapping regarding:

• SE electricity variables (change back from "net" to standard reporting variables)
• steel production now reported across technologies

Checklist:

• I did not use Excel to open csv files or checked that no side-effects occur (changed values, many new quotation marks, …)
• I added any renamed piam_variable to renamed_piam_variables.csv to guarantee backwards compatibility.
• For REMIND variables, I used |+| notation consistently. This can be achieved automatically with updatePlusUnit().

It is recommended to have a look at the tutorial before submission.