S10 reduce envelope

Implemented JS MapReduce for MongoDB:

```ruby
{       
        "posted"=>{"count"=>0.0, "leads"=>[]},
        "processed"=>{"count"=>0.0, "leads"=>[]},
        "delivered"=>{"count"=>1.0, "leads"=>["1"]},
        "open"=>{"count"=>1.0, "leads"=>["2"]},
        "click"=>{"count"=>0.0, "leads"=>[]},
        "deferred"=>{"count"=>0.0, "leads"=>[]},
        "spam_report"=>{"count"=>0.0, "leads"=>[]},
        "spam"=>{"count"=>0.0, "leads"=>[]},
        "unsubscribe"=>{"count"=>0.0, "leads"=>[]},
        "drop"=>{"count"=>0.0, "leads"=>[]},
        "bounce"=>{"count"=>1.0, "leads"=>["3"]}}
```