CRM-14319 standardise action_schedule api

CRM-14319 standardise action_schedule api
in the course of trying to write tests for this I found the api was non-standard in ways that suggested copy & paste rather than
intention. The mandatory fields said one of title, mapping_id, entity_value & entity_status - whereas it seemed to me that all
are required except entity_status, also I found that one date field was required, other changes were only legacy boilerplate

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* CRM-14319: not all scheduled reminders are being sent
  http://issues.civicrm.org/jira/browse/CRM-14319

Conflicts:
	api/v3/ActionSchedule.php