Add risky order dot to index

I think it could be useful to have a flag to recognize the "considered risky" orders. This pull request adds a "Risky" column to the orders index in admin with green dot for safe orders and red dot for risky orders.

When I run `bash build.sh` I get:

```
Failures:

  1) Spree::Api::OrdersController working with an order with a line item lists payments source without gateway info
     Failure/Error: expect(source.has_key?(:gateway_customer_profile_id)).to be false

       expected false
            got true
     # ./spec/controllers/spree/api/orders_controller_spec.rb:495:in `block (4 levels) in <module:Spree>'
     # /Users/alessio/.gem/ruby/2.1.2/bin/rspec:23:in `load'
     # /Users/alessio/.gem/ruby/2.1.2/bin/rspec:23:in `<main>'
```

but it seems is not related to my code.