Add Spree::Admin::RootController for redirecting purposes.

Currently, is really difficult to redirect to a different tab when the
user has logged in if said users cannot at least :admin, :index
`Spree::Order`s.

This commit adds a controller that handles `/admin` route so anyone can
easily redirect to another page (or implement any other logic).
Fix my mistakes from 933c773a234048b72fbd7cb4fccce8810ec55c83 :(
remove deprecated spree preferences methods from guide

introduce preferences column in spree models

add array and hash to spree preference types
Fixes #5410
Remove unused check that stubs out valid data.
Editing a shipping method was triggering to GET requests to the edit action

Add some missing preventDefault() and 'return false'
Fixes #5412
Standardizing use of colons in checkout summary
Fixes #5413
Touch Adjustment#adjustable, and fix some rspec deprecations.
Fix the damn taxes.  When tax adjustments are destroyed we need to set additional_tax_total & included_tax_total on items back to 0.

Fixes #5392
Small performance improvement calculating taxes.
fix regexp for credit card, also set month only if regexp is correct

Closes #5427
correct for value to match input id

Closes #5424
Closes #5422
User store location when signing in
Fixes #5418
Fixes #5125

Conflicts:
	core/lib/spree/core/controller_helpers/auth.rb
Fix specs broken by 09ccf8a
Fix specs broken by 87b3fa6
Include all adjustments in final shipment price

(Not solely promotions and taxes.) As per discussion in https://github.com/spree/spree/issues/5415

Fixes #5415
Fixes #5419
Fix broken specs from 4441fb42acfbf7ebf02a44c116f0d09d61c3b54f & c3a741c
refactor shipping calculator compute methods

clearer naming for methods

Fixes #5414
fix spec path in readme
Fixes #5423
refactoing code to call find_adjustment in before_action rather than calling it in each menthod
Fixes #5426