Notify a resource by the `resource[name]` key it was written as

ResourceCollection currently fills 2 functions - it keeps an ordered list of resources to converge during the 2nd Chef phase, and it keeps a unique set of known resources keyed by the resource type and name (IE, `package[vim]`).

As part of fixing https://github.com/opscode/chef/issues/1817 I am attempting to seperate ResourceCollection into two classes that encompass the different purposes.  ResourceCollection is now a thin proxy in front of these two classes to keep backwards compatibility.

**EDIT**

I am keeping all backwards compatibility for ResourceCollection.  The implementation details still utilize 2 classes for the 2 purposes.  I also made the changes to support notifying resources by the key they were written with (which was the original problem).
i'd rather this be named `:resource_set` than `:subject` because when i read `:subject` in the specs i have to rewind up here to find out what it is.  same goes for the one-liner implicit subject:

http://blog.davidchelimsky.net/blog/2012/05/13/spec-smell-explicit-use-of-subject/