Analyze partOf relations in stats

[zuphilip]

The partOf relation can occur between some publication types, but might also indicate problems with our data e.g. book is part of another book. Can we analyze the part of relations also in the statistics? I would imagine as a result something like:

{
    "partOfRelations": {
        "bookchapter": {
            "book": 6,
            "editedBook": 280,
            null: 3
        },
        "book": {
            "book": 1
             null: 41
        },
        "component": {
            "book": 28
        },
        "journalArticle": {
            "journalIssue": 1332,
            null: 25
        },
        "report": {
            "editedBook": 2,
            "reportSeries": 20,
            null: 237
        }
    }
}