add missing respond_with to some API controllers and add tests

update spec to test custom rabl template

inject custom view into dummy app

ensure usage of respond_with for orders and inventory_units

Conflicts:

	api/spec/controllers/spree/api/products_controller_spec.rb

add respond_with to ProductsController

test through custom action instead

remove fileutils
Merge pull request #5101 from themetric/fix-api-custom-template

add missing respond_with to some API controllers and add tests