Add shipping carrier integration

[bstocks]

Add support for US and Global shipping carriers.

[JobaDiniz]

Hi, I'd like to help this awesome project.
Thought of implementing Brazil shipping, which is through "Correios" api. Let me know how I can help.

[bstocks]

@JobaDiniz thanks! Anything you are interested in helping with is greatly appreciated. Region specific features are a great way to get involved. You can read more on how to get started as a contributor here: http://thoughts.reactioncommerce.com/how-to-get-involved-with-reaction-commerce/

Let us know if you have any questions, we're here to help.

[JobaDiniz]

I already read it some time ago. I have a Windows PC, so that's one problem. I'd like to implement shipping cost and shipping tracking for Brazil, but as I see, the infrastructure for shipping was not implemented yet.

Also, I'd like to implement Brazil invoices as I have experience in that area; there are a lot of things to implement in order to support Brazil invoices.

[aaronjudd]

@JobaDiniz we've implemented a shipping schema, and a flat rate example that can be used as a basic template for dynamic lookups. We'll be building dynamic methods soon, but most of the logic that you see for the flat rate lookup would similar for any implementation. We're getting ready to work on the order workflow again in the next week or so.

I'm not sure the status of Windows support, I know there are several projects that allow you to run Meteor on Windows, although I'd probably use a linux VM with a shared folder (vagrant, for instance).

[aaronjudd]

Items remaining:

• a UI for adding carrier packages (additional template type in Register) on top of basic shipping
• merge rules for merging different rate sources
• account for multi-vendor, multiple destination

[aaronjudd]

Add Shippo Package. See #421