Risk Analysis Order#is_risky? and Payment#is_cvv_risky? bugs

Addresses issues from https://github.com/spree/spree/issues/4260

- [x] `Order#is_risky?` is used in `app/views/spree/admin/orders/_risk_analysis.html.erb` partial, when it really should be checking if  `Order.payments.failed.count > 0`. As a result, when orders have 1 or more payments that have not been accepted, `Failed Payment Attempts` uses css class `.void` (a red circle) instead of CSS class `.complete` (a green circle).
- [x] `Order#is_risky?` doesn't take into account if its payments `avs_response` or `cvv_response_message` are the empty string. 
- [x] Add updated unit tests for `Order#is_risky?` method
- [x] Add logic and translations for the `_risk_analysis.html.erb` `legend` element to show whether order is risky or not.
- [x] `Payment#is_cvv_risky?` returns true if `cvv_response == ""`.
- [x] Add updated unit tests for `Payment#is_cvv_risky?` method

![screen shot 2014-01-27 at 10 03 11 pm](https://f.cloud.github.com/assets/199422/2016630/e30d2f96-87e1-11e3-8a9a-e7edfba1e6b8.png)