Wdb wrapper

Hi Bryan,

I decided that I need to add a few more primitive wrappers, namely "sketch", "extrude" and "revolve", as they are really useful and probably many people uses them. I have to admit I never used them before, creating the simplest sketch in mged needs a real steep learning curve - in this respect the work of wrapping it in python has payed off very well for me as I now understand much better how it works.

At the moment of  this writing only the sketch primitive is wrapped and works (reading/writing), I might add extrude and revolve still today as they seemed to be quite simple. Sketch is comparable in complexity with a Combination, if not worse...

Cheers,
Csaba