Refactoring search & batch

Search provides a better interface now
Batch can find orders
Batch can find items across all orders that are relevant
Order.items is now a proper object and hides 'filter' in prototype
TEMP COMMIT: Use a proxy around batch to change attributes

The application is expecting 'batch.items' to be an attribute, but the
final implementation will be a function.  In order to prove the concept
we're wrapping batch in a proxy here so that 'batch.items' calls the
function that will eventually become 'batch.items()'.
Merge pull request #30 from mattdenner/access_items_from_batch

Access items from batch