Indexer should write ElasticsearchSource objects, not protobufs

Signed-off-by: Sharif Olorin <sio@tesser.org>
Unpack contents responses to ElasticsearchSources

Signed-off-by: Sharif Olorin <sio@tesser.org>
Expect ElasticsearchSources in chevalierd's indexer

Signed-off-by: Sharif Olorin <sio@tesser.org>