Will now test sample using a chain of rake tasks

So that a) we can observe the complete output and b) we can actually debug it
Changed order of installation to fix dependency error when performing a new installation
Place shared ability examples in testing_support for extensions to access.

Fixes #2834
Default frontend+backend locales to Rails.application.config.i18n.default_locale, rather than 'en'

Fixes #2825
Remove invalid duplicate line-items id in shared/_order_details.html.erb

This has now been moved to the <table> tag which contains both these elements.

Fixes #2836
Fix unshippable items table color in checkout/delivery

Fixes #2820
Fix shipping instructions style.
Remove rate_hash reference.

It no longer seems to exist.
[backend] Require correct bar_ability file within admin/orders_controller_spec
Throw an error if db:migrate runs with spree_sample:load

This is because running these two tasks at the same time produces an error:

http://ci.spreecommerce.com/viewLog.html?buildId=2490&buildTypeId=bt28&tab=buildLog#_focus=335