If one chooses regression and pred col is binary, throw error

[levithatcher]

This is the current unhelpful message: ValueError: Unable to parse string "N" at position 0

Set error (with helpful message) when classification is chosen and pred col is numeric

[Aylr]

While working on a fix for this problem I discovered a few related problems:

1. a classification run on a non-binary column
2. a classification run on a binary column who's unique values are not 'Y' and 'N' (for example: GenderFLG)
3. a regression run on a column containing non-numeric data

I'm wondering if it is good enough for now to cover the original issue and the identified issue 1 above, and simple print a helpful error for 2, 3.

[Aylr]

Relates to #265