Remove the duplicate code caused by 'max_opacity'.
GaussianOpacityNode actually generates a Gaussian now. Woo.
Add scipy to the TravisCI config
Define the Gaussian min radius where it's needed.

As an added bonus, fix the radius double counting weirdness that was
making the radius resizing and other movement wonky.
Get the mouse pointers correct for better Gaussian resizing UX.
Merge pull request #31 from enthought/refactor/gaussian-opacity-node

Clean up GaussianOpacityNode