Allow running pade from bin dir without PYTHONPATH
Add some job validation

+ Raise UnknownStatisticException if we get a statistic
  we don't know about
+ Raise UnsupportedLayoutException if the combination
  of statistic and layout is not valid.
Add some more validation

Make sure we don't equalize means with a statistic that
won't work with equalized means.
Fix a couple minor bugs