[STORE] Added the `find_each` method for models

    Person.find_each { |person| puts person.name }

    # # GET http://localhost:9200/people/person/_search?scroll=5m&search_type=scan&size=20
    # # GET http://localhost:9200/_search/scroll?scroll=5m&scroll_id=c2Nhbj...
    # Test 0
    # Test 1
    # Test 2
    # ...
    # # GET http://localhost:9200/_search/scroll?scroll=5m&scroll_id=c2Nhbj...
    # Test 20
    # Test 21
    # Test 22

See: http://api.rubyonrails.org/classes/ActiveRecord/Batches.html#method-i-find_each