CRM-12545 fix tests broken by work on activity contact restructuring
CRM12547, CRM-12357 fix Mailing Contact api to comply with api conformance tests
fix includes -
- using spec function to provide documentation, enforce required fields, provide default, enforce options
- using standard api function to process 'limit', 'sort' etc
- skipping checks for getByID because in this area the api cannot be made standard
NOTE that the default limit has been set to the api default (25). Making
this non standard for a particular use-case doesn't make sense.

Preferred calling method is
$params['options' => array('sort' => 'contact_id DESC', 'limit' => 50,
'offset' => 200)