Added in new method of statistics calculation for train/test
classification which is enabled by the new test document data
structures.
Made "getTrainTestEval(Instances train, Instances test)" an abstract
method of Analyzer. Moved current logic into WekaAnalyzer. Other
Analyzers do not currently support the new statistics generation.
Fixed a bug where unknown documents were not properly removed
Switched in new Eval references/handling. Removed some obsolete methods