Create 8 direction folding animation for Plasma Turrets

[KiwiHawk]

Plasma turrent folded_animation, preparing_animation, and folding_animation were disabled by #77 due to no 45 degree animation. Reenable these plus supply new animations for the new four directions.

[KiwiHawk]

@Qatavin FYI: I've logged this issue for reimplementing the removed animations.

[Qatavin]

I'm certainly all for it. I didn't try before because it appeared to be rather complicated for me. Hopefully a more experience sprite artist can take a whack at it.

In the existing 4-directional animation in question, there are 15 frames in total.

1 for the resting position.
6 for extending the leg. - Actually, only the lower part of the leg moves. The top part remains at a constant angle.
4 for pulling back the cover.
4 for extending the sight.

Fortunately, the head of the turret does not cast a shadow on the foot of the rotating part, so that's one complication avoided. The power cable in the back would take a bit of redrawing, but nothing terrible. I'm not sure how to go about making the shadow layers, though.