Added CoSE Layout

Added CoSE Layout. 

Implemented by Gerardo Huck as part of Google Summer of Code 2013.
Mentors: Max Franz, Christian Lopes, Anders Riutta, Ugur Dogrusoz.
Based on the article "A layout algorithm for undirected compound graphs" by Ugur Dogrusoz, Erhan Giral, Ahmet Cetintas, Ali Civril and Emek Demir.