Thick Wall Insulates

Makes thick walls (3+ cells) actually insulate, instead of acting like 1-cell thin wall (almost) directly to the outside.

Vanilla behavior (without this mod):

1-cell thin wall moves current room temperature towards temperature of the room on the other side.

2+-cell wall moves current room temperature towards OUTDOOR temperature (NOT temperature of the room on the other side of the wall!) at half-speed.

With this mod:

1-cell thin wall moves current room temperature towards temperature of the room on the other side (like vanilla).

2-cell wall moves current room temperature towards temperature of the room on the other side of the wall at half-speed if the outer wall is only open on one side, or at 3/4 speed if it's open on 2 or 3 sides (wall corners are useful now).

3+-cell wall actually insulates and does not affect room temperature at all.