Allow managers to remove line items from order

Managers of an order cycle and the distributor of an order are allowed to
remove a line item from the order.

app/controllers/spree/admin/line_items_controller_decorator.rb

@@ -0,0 +1,8 @@
+Spree::Admin::LineItemsController.class_eval do
+  private
+
+    def load_order
+      @order = Spree::Order.find_by_number!(params[:order_id])
+      authorize! :update, @order
+    end
+end

app/models/spree/ability_decorator.rb

@@ -144,6 +144,9 @@ class AbilityDecorator
     end
     can [:admin, :bulk_management], Spree::Order if user.admin? || user.enterprises.any?(&:is_distributor)
     can [:admin, :create], Spree::LineItem
+    can [:destroy], Spree::LineItem do |item|
+      user.admin? || user.enterprises.include?(order.distributor) || user == order.order_cycle.manager
+    end
 
     can [:admin, :index, :read, :create, :edit, :update, :fire], Spree::Payment
     can [:admin, :index, :read, :create, :edit, :update, :fire], Spree::Shipment