Skybox 

Creation of The Skybox Class which render a skybox for the 3D scene.

This is the list of thing added to the project : 

- Skybox.hpp and Skybox.cpp (/glimac/....)
- cubeMap.vs.glsl and cubeMap.fs.glsl (/shader) since we are using cubemaps to bind the textures we need customs shaders
- testSkybox.cpp (/tests) a test file
- 6 PNG files for textures (assets/textures/skybox)

And as Adele would say : 

Let the skybox (let the skybox)
When it crumbles (when it crumbles)
We will stand tall (we will stand tall)
Face it all together
At skybox

cleaner in ~Skybox() destructor