Simplifies the dist zip file to remove the top level js and css
directories. Reduces the complexity of the dist target in the build
file.

Contents are now:
    simplicity-{version}/simplicity.js
    simplicity-{version}/simplicity.min.js
    simplicity-{version}/simplicity.css
    simplicity-{version}/simplicity.min.css
    simplicity-{version}/images/first_vertex_29x29.png
    simplicity-{version}/images/vertex_29x29.png