Re-organize all projects (#4166)

Content.Shared/Gravity/GravityChangedMessage.cs

@@ -0,0 +1,18 @@
+#nullable enable
+using Robust.Shared.GameObjects;
+using Robust.Shared.Map;
+
+namespace Content.Shared.Gravity
+{
+    public class GravityChangedMessage : EntityEventArgs
+    {
+        public GravityChangedMessage(IMapGrid grid)
+        {
+            Grid = grid;
+        }
+
+        public IMapGrid Grid { get; }
+
+        public bool HasGravity => Grid.HasGravity;
+    }
+}