Add more CNC stuff

I added two new textures for the active mode.
Also it can now change program while active without emptying the input slot first.

I believe the CNC addition is ready for the master branch now.

I am considering the API if it should be possible to come with a custom nodebox shape and image or not.
I would also like some shapes to build both Roman and Gothic arches. That however would require a new design of the program part of the formspec to allow more pages. And I don't know how to do this...