Improve input attach points for multi-input gates

[cdwfs]

Gates with two inputs (AND, OR, XOR, etc.) should have their attach points at the usual points at the corners, not in the center.

It's probably worth specializing the authoring for Not vs. And/Or/Xor vs. Sink (1 input, 2 inputs, N inputs).

[cdwfs]

Fixed by 43ef9c9