add getTotalItems() and fix limit method so PaginatedList works

Currently we can't pass Totalitems to PaginatedList() from Elastica\ResultSet->getTotalHits();

Example:
$result = ResultList::create($index, $query);
$result->limit(10,(int)$this->request->getVar('start'));			
$list = new PaginatedList($result);
$list->setTotalItems($result->getTotalItems());