Update Grafitti-simple to use Ojwidgets and remove o'Closure.

This commit also fix some stuff regarding values injection, to follow the latest version of Eliom.

Since we can expect the next release of Eliom to be soon, I updated Graffiti simple (used in the tutorial) to the latest version of Eliom.
I also removed O'Closure, since nobody in here really want to compile it anymore.
I replaced it by a simple HTML5 slider and a custom colorpicker added in Ojwidget for the occasion.

This is a work in progress, I still need to fix some stuff and I think i'll try to split up this commit soon, but I want some feedback to be sure that I don't do something wrong here. :-)

The code needed to be a little changed, since the colorpicker is now different, I prefered to send a tuple for RGB values instead of a string, and let the client and the server do whatever they want with it.