Show log entries in the admin backend

Working towards a solution for #3978
[backend] Fix issue where database cleaner was not truncating tables
Bump kaminari to 0.15.0
Go with whatever money gem activemerchant depends on
Touch shipment when IUs are updated, and touch order if Payments or Shipments change
Remove extra line from ResourceController#model_class that was added in #3974

This line causes this issue: https://github.com/spree/spree/pull/3974#issuecomment-29130309
Stub touch on mocked Order in shipment_spec
Don't override accessor if model has column already

Say users want to add a `name` column in spree_variants. They can't make
use of that attr on a variant instance because Spree would always
delegate that method to a product.

Now it would only delegate if the model doesn't have that column. That
would be all cases in a default scenario.

Fixes #4012
Move ::Money.extract_cents and ::Money.parse to Spree::Money, as those methods are being deprecated and we care about them.

Conflicts:
	core/lib/spree/money.rb
Add missing link for log entries
[backend] Use display_amount to display payment amount in payments/show
Include UTF-8 encoding in money.rb
add translation for canceled shipment state

Fixes #4005
Set up a Spree.routes.root property via js

Provide the application a global accessor for the root path in js as
stores are not always mounted on the root domain "/"
[backend] Persist 'only show completed orders' checkbox across pagination requests

Fixes #4004
Add changelog entry for #4004
[api] Add tentative caching to the parts that make up an order
Add changelog for order caching speedups
Use a more sensible method to get log entry partial name
When removing defunct zone members use classify instead of capitalize when deleting zone members by zonable_type.

When creating a custom zone member type like zip_code for example using capitalize removes all models with zonable type != Spree::Zip_code instead of Spree::ZipCode

Fixes #4001