Fancy imshow and colormixer refactor complete + more functionality

[Chris Colbert]

Hey Everyone,

I think i've fixed all the problems I mentioned last night concerning
the circular references, etc...

In the process, I managed to speed up the widget quite a bit by
getting rid of unnecessary fluff.

I've also added gamma correction and sigmoidal gamma correction to the
color mixer and the imshow widget.

So if you all would be so kind, please grab it from my IO branch and
give it a thrashing, and let me know if anything breaks.

I'm gonna get working on fixing the aspect ratio, and usings holgers
suggestion of being able to hide widgets...

Cheers!

Chris