"Scope by property" for filters

While the Scope by Property feature is useful, it assumed that all events in the workflow share a similar property on all the events used. There are many cases where an event might trigger a workflow and all event queries for the _same_ event in the workflow should be scoped, but references to other event types might not want to be scoped. EX: favorite_item event with a 'category' (shoes) property. That workflow might want to see if the user had favorited any other event in that category, __and__ if that user has ever triggered the referred_friend event. Based on that conditional maybe we want to prompt them to take the referral action. But as-is we are unable to query the referred_friend while scoping that favorite_item query too.