Adds LastTupleFromBag to match datafu's FirstTupleFromBag. Moves KV converters. Removes up obsolete Session UDF, as datafu contains this.
Merge branch 'master' of github.com:wikimedia/kraken
Breaks KV utils (for cookies, x-analytics) out of UDF.
Refactor KV UDFs.
Session script works perfectly except for x-analytics parsing.