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

To use the LWJGL back end, use the command:
sbt "backendExamplesLwjgl/run 2"
(you can replace 2 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 elegeant)
We originally planned to have this done interactively, by presenting the different choices in the standard output and using the console to let the user choose which demo. But we faced a bug when running the demo from SBT: any attempt to read the standard input acted like we reached the EOF (it worked fine when we tried to run the program using directly scala with the CLI).