Add ability to export career matrix as CSV

Also refactoring to allow the career matrix transformations to be unit tested.

Also here is the CSV it generates engineering_ic_career_matrix.csv

For the time being this data URL is around 9k bytes. A data encoded URL should handle up to 64k bytes so we may wish to choose a different option in future. I suppose it could also be zipped up in the data encoded URL as well. Alternatively creating this as a CSV file somewhere and just linking to that may be more sensible but I didn't actually know how to do that.