Cleanup, external conf and better handling of yahoo data (avoid duplication due to closing hours)
* dedicated conf object for configuration stuffs
* SparkAkk object'ed and use of configuration stuffs to start
* use env var for twitter oauth inf application.conf
* yahoo actor now checks if new it's a new data that it's receiving or a already received one. In the first case, it published in the DStream
* yahoo is now aked different information in the csv -- like the changes decoupled and the validity of the tracking name

>> should now be time to unify both streams and to apply windowed computation...