Analyse the event stream to find documents modified by a spammer

Right now when we find a spam author we try to find all pages he/she has modified by using SpamCleaner#getDocumentsForAuthor(). However that only checks if the spammer is the creator or the last author of documents.

We also list all the events done by that spammer.

However, we could do better and analyse the events done by that spammer to find documents that he/she has modified, even if there have been other modifications after their changes.