Separate the model mapping functionality into its own lib

The model mapping framework should be usable by other clients such as Sear. Therefore we need to separate it into it's own library.
The plan is to first create a new library, proposed name "Ares", and put the code in there. If it works out nicely it might then be moved to the Eris library.
The code is clean and have no dependencies on Ember specific functionality, so there should be no real problem moving it.
However, we need to decide whether we also should include the model mapping xml serializer. This adds a dependency on TinyXML, but that's something that Sear already uses.