patching bug on experiment runner
Merge branch 'i28-indexerror-on-weighted-classes' into develop
when all columns are removed, instead of ValueError, MoreSamplesNeededException is raised
when MoreSamplesNeededException is raised, fact_extraction is skipped that round
Merge branch 'i29-keep-running-if-all-columns-are-killed' into develop
removed unneeded import
added definition of round 6 of experimentation, with specific classifiers
making all iepy configs for round6 to use drop-mode. And small docstring changes