Fix dynamic templates

dynamic templates didn't work anymore resulting in config validation exception:
1. they are a list of hashes: The previous logic for this was removed in the extension https://github.com/FriendsOfSymfony/FOSElasticaBundle/pull/629/files#diff-e0950e36ea63dd2c4b5151242670298cL275
2. they require a `mapping` key (not propeties as broken by https://github.com/FriendsOfSymfony/FOSElasticaBundle/pull/629/files#diff-850942b3ba24ab03a40aaa81b6152852R262)

See http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-root-object-type.html#_dynamic_templates