Integrated Relationship miner

* extended Twitter User Repo with readAll
* bringing both relationship and streaming statuses miner to work

Things to improve:
* I fall back to using an embedded neo4j database, because the server/embedded
  modes differ, such that I cannot use the current implementation with a server
  database. This has to be changed though in future.
* the RelationshipMiner does not take care of rate limits for Twitter API.
  I think this would be though a bug in the twitter4j library, but we have to
  fix this in our implementation
* The RelationshipMiner should use the last_synched field in TwitterUser in
  order to avoid crawling the same users when restarting the app.
* The SqlUserRepository save method needs to take care of create or update (the
  merge feature is not supported in postgres...)