Centering doesn't take direction (`direct=`) into account

[Equidamoid]

The centering code always assumes no direction is specified (e.g. to center a cylinder, you translate it by (r, r, -h/2)). For example, cq.Workplane().cylinder(10, 10, (1, 0, 0)) will create a cylinder with axis going from (0, 0, 5) to (0, 10, 5).

Since proper direction handling is a bit tricky, how about at least throwing NotImplementedError if centering is requested when direction is not (0, 0, 1)? This will at least save users some headache debugging suddenly shifted parts (speaking form experience).

[sensille]

I'm very new to cadquery, but I think I also ran into this issue.