Adds tracking_url field to shipping methods

This feature adds the ability for tracking numbers to be clickable throughout
the system.

Without it, the customer needs to locate the tracking website themselves and
copy and paste the tracking number (except gmail users). It also effects admins
who are trying to investigate the history of a shipment, it would be helpful if
they could just click on the tracking and open up the tracking site.

Fixes #2644
[sample] Add missing spec folder
Revert "adds threading to chain of shipping_method.compute calls"

This reverts commit a582903d71e96ea2e0816be2e46587ce9ea8a40f.

This reverts PR #1976.

This fixes #2429.

Conflicts:
	core/app/models/spree/order.rb
Stop using @order in favor of order

order is passed as a local in every instance this partial is called

Fixes #2648
updates jquery.live to .on for jquery 1.9

Fixes #2677
Fixing locked orders due to invalid card details for a payment

Fixes #2616
Fixes #2570
Fixes #2678
Fixes #2585
Fixes #2652
Correct call to available_shipping_methods within Order#rate_hash
Display multiple payment information on the order confirmation/complete page

Related to #2616 and its related issues
[api] Remove Order#payment_method reference inside orders/payment.v1.rabl
Allow tracking_url to be mass-assigned for ShippingMethods

Fixes this broken build: http://ci.spreecommerce.com/viewLog.html?buildId=671&buildTypeId=bt6&tab=buildLog
to suppress the error from the log, check for column names before executing SQL

Fixes #2681
Set Spree::Config[:default_country] in countries seeds, rather than setting it to a magic number in app_configuration
no need to stub WebMock things in sample tests
Minor cmd README.md upgrade.

reformatted options for Git

Fixes #2688
Move mailer tests from frontend to core
Reload line_items association in order_with_totals factory so we can access it afterwards
Overhaul CheckoutController spec
Stub tracking_url in shipment mailer spec to fix specs
Fix issue where entering a number greater than 2,147,483,647 would throw a server error

Fixes #2695
[frontend] Correct test blocks inside checkout spec