[Streaming] Examples using Twitter's Algebird library

This PR adds two examples for streaming that use monoids from Twitter's Algebird library:

* HyperLogLog for approximate distinct object counting with low memory overhead
* CountMinSketch for approximating object frequency in a stream as well as TopK or "heavy hitters" estimation

See https://groups.google.com/forum/?fromgroups=#!topic/spark-users/4ht9ndVaZQY