Added test_helpers module

Removed a bunch of duplicated code from test scripts
Made false negative tests more precise

Also added some more comments to test_helpers
Scoring changes and test cleanup

Fixed bug in Scorer where window length was not used to compute relative scores.

Made some tests a bit more stringent.

Improved comments.  Misc test cleanup.
Merge pull request #35 from subutai/score_testing_cleanup

Score testing cleanup
Merge branch 'master' of github.com:numenta/nab