Fixed confusion between test mode and sandbox environment

The authorize.net AIM service allows for two modes of operation, "Live" and "Test." Each mode can be used within a production or a sandbox authorize.net account. Sandbox accounts are used by developers for testing purposes.

The authorizeaim module incorrectly equated the "sandbox" environment with the "test" mode, meaning that selecting "Test" would send the transaction to the sandbox API endpoint, and also include the 'test' post variable in the request.

This pull request fixes this issue by allowing the admin to select which type of authorize.net environment they are using, AND which mode should be used.

More info from authorize.net:
https://developer.authorize.net/guides/AIM/wwhelp/wwhimpl/js/html/wwhelp.htm