add "free children from part" pace tool

pac editor tool "free children from part" will take all the children of
the currently selected part, offset their angles, position, angle
offset, and position offset by the values their parent gave them, then
set their parent to their grandparent. This in effect makes them have
the same position on your costume but removes them up a level in the
hierarchy. This is useful if you have built something using one part as
a reference point for many other parts, and would now like to remove the
reference point and "hardcode" the values into the individual parts.