Per-map parallax support (#9786)

* Per-map parallax support

* Comments for future sloth

* c

* bet

* Fix exception

* VV support

* Fix parallax

* mem

* weightless sounds

* Gravity stuff

* placeholder coz im too lazy to stash don't @ me son

* decent clouds

* sky

* Fast parallax

* Imagine spelling

* Loicense

* perish

* Fix weightless status

Co-authored-by: metalgearsloth <metalgearsloth@gmail.com>

Content.Shared/Gravity/GravityChangedEvent.cs

@@ -0,0 +1,15 @@
+namespace Content.Shared.Gravity
+{
+    public sealed class GravityChangedEvent : EntityEventArgs
+    {
+        public GravityChangedEvent(EntityUid changedGridIndex, bool newGravityState)
+        {
+            HasGravity = newGravityState;
+            ChangedGridIndex = changedGridIndex;
+        }
+
+        public EntityUid ChangedGridIndex { get; }
+
+        public bool HasGravity { get; }
+    }
+}