Added Users controller to API

Conflicts:

	api/app/helpers/spree/api/api_helpers.rb
WIP Ability changes to allow record level permissions
Add instance level permissions in Admin controller  /
ResourceController, and encourage more use for CanCan's
accessible_by method. Re-adds ability specs that were in
spree_auth_devise
Drop admin user controller
Show variant images in admin/images if that's all there is

Fixes #2228

fix
Tidy up Close/Open button UI in admin/adjustmnets
Fix clearing floats on admin/shipping_methods _form partial. Fixes #2472

Fixes #2509
Fix broken split prices migration.

The migration will attempt to populated spree_prices with
the variant price.  Unfortunately, since variant price is
now delegated to spree_prices, it will come back as 0.

Instead of reading from the variant price method, it's
going to set the price based upon the actual column value.

Fixes #2477
Fix SEO title again

Related to #1912 + 8eff78f1acc85194ce9e5289a8bf9159da447fdf
Remove call to authorize! which is actually not doing anything

Thanks to @laurens
Fix broken link for general settings in general_settings/edit

Fixes #2469
Do not assign params in ResourceController#build_resource

Assign params in ResourceController#create instead (same location as ResourceController#update)

Fixes #2483
Introducing sortable product properties.

Fixes #2464
change icon class for delete icon so it's visible on zones/states page

Fixes #2489
Use a string comparsion for locale parameters
Allow a returned item to be re-shipped

Fixes #2475
Fix for improperly namespaced url in admin

Without this change controllers which are:
a) outside of the Spree module namespace and
b) inherit from Spree::Admin::BaseController and
c) are routed inside the application's routing, not Spree's

will not be able to determine the url and their views will not
compile.

Fixes #2500
[api] No need to convert template name to symbol when rendering RablTemplate
Use relative link support for link to build.sh

Fixes #2505
Updated README instructions

* Removed annoying $ so that instructions can be copy-pasted.
* Added appropriate syntax highlighting.

Fixes #2506