Change offset behaviour when viewport bounds change size

[Flojo101]

Instead of expanding (or contracting) the right and bottom edges of the netlist (the top left corner stays fixed), it would perhaps be an improvement to instead keep the current of the current viewport in the center of the viewport after the bounds change. This would mean that both the left and right as well as the top and bottom edges contract symmetrically. The behaviour itself could be toggled by a setting to allow the user to control this