first round of fixes

FindAwesomium and AWESOMIUM_LIBS added/fixed
OS.h include wglew.h is now guarded from *nix
removed Sigma_LIBS from cmake (unused)
ADDITIONAL_LIBS is now ADDITIONAL_GLFW_LIBS in cmake
compiles and runs on ubuntu 13.04

- glewExperimental = GL_TRUE
- X11 and other odd GLFW dependencies linked in cmakelists