Re-organize all projects (#4166)

Content.Client/Markers/MarkerSystem.cs

@@ -0,0 +1,27 @@
+using Robust.Shared.GameObjects;
+
+namespace Content.Client.Markers
+{
+    public sealed class MarkerSystem : EntitySystem
+    {
+        private bool _markersVisible;
+
+        public bool MarkersVisible
+        {
+            get => _markersVisible;
+            set
+            {
+                _markersVisible = value;
+                UpdateMarkers();
+            }
+        }
+
+        private void UpdateMarkers()
+        {
+            foreach (var markerComponent in EntityManager.ComponentManager.EntityQuery<MarkerComponent>(true))
+            {
+                markerComponent.UpdateVisibility();
+            }
+        }
+    }
+}