Fix Dataset issues so it will work with new census samples (coming later): (#95)
Fix Dataset issues so it will work with new census samples (coming later): (#95)

1. deal with whitespace for numeric columns
2. for regression scenario, plot target column as well if specified. Right now it doesn't because we mistakenly prepend "target" and it becomes non-numeric column.

Tested current Iris and Census samples.
jdanbrown/pydatalab,jdanbrown/pydatalab,jdanbrown/pydatalab,parthea/pydatalab,craigcitro/pydatalab,supriyagarg/pydatalab,yebrahim/pydatalab,googledatalab/pydatalab,craigcitro/pydatalab,yebrahim/pydatalab,parthea/pydatalab,supriyagarg/pydatalab,parthea/pydatalab,supriyagarg/pydatalab,googledatalab/pydatalab,googledatalab/pydatalab,yebrahim/pydatalab,craigcitro/pydatalab