Drop order decorator / after commit shipment updates

This was still causing infinite loops via Wombat as everytime a shipment
is updated an order is updated as well which in turn will update the
shipment timestamp again and it will keep getting pushed to Wombat
forever ..
Tweak gemfile for easier bundling and postgres

Without coffee and sass I was getting version conflicts with spree
backend
Fix couple product handler specs
Serialize payment source data.

Specs added for SourceSerializer.

Fixes #17
Example setup should default to filtering complete orders.
Make sure we set the provided shipment id from the payload received as the shipment number
Merge branch '2-3-stable' of https://github.com/spree/spree_wombat into 2-3-stable