Detection Features

I added a Detect feature for the GUI via 2D cross correlation.  Allows
the user to go through brain data, crop out selection to be used for
correlation, and input top cutoff percent for correlation process.  The
GUI implements correlation with entire image stack.
Crop and Histogram

Added cropping and histogram features to GUI.
Merge pull request #2 from openconnectome/CorrelationGUI

Correlation gui