Commerce OO

This is a WIP for some object-oriented classes that wrap Drupal Commerce entities such as Order, LineItem and Product. They're designed to be simple and light weight and offer a few benefits:

1. Makes testing your own code that relies on Commerce entities much easier.
2. Simplifies getters/setters rather than using field api and entity_metadata_wrapper functions.
3. Allows you a base to extend if you want to enforce specific actions or rules on the entity.