Don't check for variant availibility before determining which thumbnails to show
Edited extension templates to require frontend/backend assets instead of spree_core

Fixes #2849
Fix issue where a product with no shipping category would crash checkout

Fixes #2804
[frontend] Navigate to root path before attempting taxon specs
Use taxon name on taxons/show rather than its accurate_title
Convert state in Payment.with_state to String before calling where

Fixes this issue: https://gist.github.com/swrobel/e574a0d317f4474e86f3
Use taxon name on taxons/show rather than its accurate_title

Fixes #2814
Making newly entered payments invalidate previously entered payments so the most recent payment is used by the gateway.

Fixes #2828
Bump shoulda_matchers to latest version.

Fixes #2840
Add line breaks after each shipment and payment.

Fixes #2842
Add helper methods to shipment to calculate shipments item and total costs.

Fixes #2843
Fix last_incomplete_spree_order to return 'last' order
Remove user class extensions duplicate file from frontend
Add note about formatting
Factor product scopes to allow simple scopes to be added from an extension

Fixes #2608
Fixes styling issue where email is pulled left out of the info area.

Fixes #2850
Remove shoulda-matchers entirely

It doesn't seem like we're using this anywhere.
Fix shipping methods showing up multiple times in admin
Switch the mailers to be invoked using ids, not model objects. This makes it easier to support asynchronous mail jobs, as only simple ids need to be persisted.

Fixes #2808
Better factory integration for extensions.

Related to #2780