Effects update

Removes /obj/effect/projection and /obj/effect/shut_controller. Amends the name of /obj/structure/showcase to be lowercase.

Moves /obj/effect/decal/mecha_wreckage to /obj/structure/mecha_wreckage. Does not update the map.
Standardises and updates text styling in mecha_wreckage.dm.

Moves /obj/effect/alien to /obj/structure/alien. Does not update the map.
Moves /obj/effect/alien/acid to /obj/effect/acid. Adds a new sprite for acid.
Standardises and updates text styling in code/game/objects/effects/aliens.dm.