add a offset parameter to extrude

[cssi-dev]

I am new to this project. I spent a lot of time in AutoCAD, Inventor, Fusion and Solidedge and the main feature I am missing is a optional offset parameter for the extrude function so that I no longer need to draw exactly the same sketch a bit above the other one. That also enables drawing the sketches first and then extruding them afterwards.
I think one number should do the trick, to create a distance between the part and the sketch.