Fixed StatisticsListDisplay Output

It used to remove the last 2 characters in every line, but now it doesn't.
Minor Fix to StatisticsListDisplay Header Alignment
Significant Fixes for IntervalNGramStatistics

- fixed IndexError when the n-gram finder would go off the end of the
  AnalysisRecord
- fixed xrange() calculation error (on my part) where 2-grams were built
  with a vertical interval and the same vertical interval, rather than
  the a v.i. and the next one
Experiment Subclasses Know Their Controller

I added an argument to __init__(), so an Experiment knows its controller,
which means errors can be sent through its error() signal.

Also other minor clean-up things.