Utils for texture & main loop + Back ends examples

To see the examples using the WebGL back end, use the command:
sbt "backendExamplesWebgl/optimizeJS"
and open the file backend-examples-webgl/index.html with your favourite web browser [1]

To use the LWJGL back end, use the command:
sbt "backendExamplesLwjgl/run 2"
(you can replace 2 with the number of the example you want to see, between 1 and 5 for now)

Note that the example 5 "render-to-texture" require OpenGL 3.0. So if you use a Intel IGP older than a Sandy Bridge, LWJGL will probably refuse to create the context (but we had it working with an Arrandale when using Linux 3.11 and a OpenGL 2.1 context, it's just not very elegant)

[1] Chrome and Chromium work fine. However, their security policy is more strict than Firefox when it comes to local files and you may need to start your browser with the parameter "--allow-file-access-from-files" to have the texture loading properly. And our examples don't work in IE11 for now (couldn't figure the exact reason).
You should use the `for`-comprehension on `Program` to use a program.