Parametric stackable sieve

This is a remix of [A parametric sieve with 3 example STL's](https://www.thingiverse.com/thing:754365), it was a nice basis, but the holes were not working really correctly if you changed the bottom thickness, they can even end up not being holes at all.

So while I was fixing the holes problem, I added a nice collar to make it stackable.

### Edit 2018-06-04:

Fixed an off by one (too much) error in the number of holes it would generate. Holes would begin under the frame. It would only happen in some corner cases and when the holes are big enough for it to be seen.