Add scikit-learn HW7

I compare RandomForest, LDA, SVC and kNN results to the baseline results for exercise #1, and I compare RandomForest and kNN results to the baseline results for exercise #2.

**NBViewer:** http://nbviewer.ipython.org/github/cosmoharrigan/2014_Astr599_HW/blob/HW7_branch/cosmoharrigan/HW7.ipynb