"date". accepted values are '!=', '>', '>=', '<', '<=', '='.
* 'modified' => NULL - the date the action was last updated. Expects a DateTime object, a unix timestamp, or a string that can parsed with strtotime(). Used in UTC timezone.
* 'modified_compare' => '<=' - operator for testing "modified". accepted values are '!=', '>', '>=', '<', '<=', '='.
* 'group' => '' - the group the action belongs to.
* 'status' => '' - ActionScheduler_Store::STATUS_COMPLETE or ActionScheduler_Store::STATUS_PENDING.
* 'claimed' => NULL - TRUE to find claimed actions, FALSE to find unclaimed actions, a string to find a specific claim ID.
*