Maint/puppet 4/document event manager

This adds documentation to `Puppet::Transaction::EventManager` and `Puppet::Resource::Status` and removes some dead attributes from `Status`.
This is where the resource was added to the catalog:

```
[1] pry(#<Puppet::Resource::Status>)> @file
=> "/home/adrien/eng/projects/platform/puppet/ex.pp"
[2] pry(#<Puppet::Resource::Status>)> .cat ex.pp
# ex.pp
notify { 'hello': }
```

So this is the declaration then?