TS-938 - Don't merge

Adding the config and a gen_server to handle the c* nodes. But this uses elysium 0.1.7 so the files changed are really misleading.

Also the query seems to work, but it is not currently being used.
Right now cassandra_nodes() returns [cassandra_node()]. I think this should be elysium_config:cassandra_seed/1 and should return cassandra_node(). There's no need to parse a binary every minute. The config stuff was intended to be fast, without locks and as close to the needed information as possible.