Change exports to be nested arrays rather than entity_import'd JSON objects

While working through how to handle an issue in Commerce (#1864186: Optional load API keys & settings using variables) I realized how Rules handles its exportables and then realized that the exportables are handled completely differently to every other Drupal exportable. Every other Drupal exportable is saved as a nested array or StdClass, and can be readily customized as needed; this allows for easy customization of default configurations used in distributions, etc, and allows for readily reusable configurations. Rules definitions, however, are created during hook_default_rules_configuration() via entity_import(), so trying to customize a mostly undocumented object makes building reusable constructs much more complicated than they need to be.

My recommendation for what should happen:

• The hook_default_rules_configuration() definitions should just contain the definitions, e.g.:
  

    $items['rules_my_authnet'] = array(
        "LABEL" => "Credit Card (Authorize.Net AIM)",
        "PLUGIN" => "reaction rule",
        "TAGS" => array
          "my rules",
        ),
        ...
  

• Whatever triggers hook_default_rules_configuration should be updated to support the current system but also the new exportables method; this should be simple to do, just check to see what each element is and handle it accordingly.

Advantages to this:

• The exportables would actually be easily customizable via hook_default_rules_configuration_alter(), which they are not today.
• It would be much easier to tailor Rules definitions, as required for Commerce to work, thus make Rules-heavy distributions more customizable without requiring vast amounts of configurations to be left in an overridden state.

Downsides to this:

• Exportables from the newer versions would be incompatible with older versions of Rules.