Add activity_type_id to case_type api output

That makes sense, but in that case what's the point of the foreach loop? Since $activityTypeXML is flat (and therefore casting to an array would work fine), we could just do the typecast... OR we could get rid of all 4 lines and replace them with `$definition['activityTypes'] = (array) json_decode(json_encode($xml->ActivityTypes->ActivityType), TRUE);`
(I added the extra typecast for good measure, in case the xml object is NULL for some reason.