[xmonad] The new decoration framework has been pushed

Hi, I've just pushed the new decoration farmework, with the floating layout, the keyboard manipolation framework, and everything I've been talking about lately. I'll try to be as quick as possible in fixing bugs. I've also pushed the LayoutCombinator class. This is will make LayoytModifier(s) and LayoutCombinator(s) implementations totally independent from the Layout implementation. I'll write more extensively on that at a later time, also because I've already said quite a lot in previous messages. Hope you'll enjoy. Andrea