Duplicate variants when duplicating products.

Cherry-pick of 69f785d732e2f7a3ad129095044413a58a97e32f

Fixes #4339
enable variant view in api. variants list is already accessible, and show method already defined on variants
controller, so no reason not to expose this

Fixes #4336
Ensure prices with currencies displayed do not break variant radio buttons on cart form

Fixes #4342

Conflicts:
	frontend/app/views/spree/products/_cart_form.html.erb
Bump to 2.0.9
Bump to 2.0.10.beta
Fix version numbers in changelogs
[api] Attempt authorization for an order if an order token is passed

This stops the 'You must specify an API key' error message from (incorrectly) appearing. That message is now supressed if an order token is passed in.

When an order token is passed, the authorize_for_order filter is called, which attempts to find an order and then compares the order's token with the order token from params/headers

Conflicts:
	api/app/controllers/spree/api/base_controller.rb
	api/app/controllers/spree/api/line_items_controller.rb
Merge branch '2-0-stable' of https://github.com/spree/spree into 2-0-stable