Add Scene with systems

- Add Scene class which populates the engine with Systems which handles
  all logic in the game
- Add Systems to ecs

CopiumEngine/src/copium/ecs/System.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "copium/ecs/ECSManager.h"
+#include "copium/ecs/SystemBase.h"
+#include "copium/ecs/Entity.h"
+
+namespace Copium
+{
+  template <typename... Components>
+  class System : public SystemBase
+  {
+  public:
+    void Run() override
+    {
+      manager->Each<Components...>([&](EntityID entityId, Components&... components) { RunEntity(Entity{manager, entityId}, components...); });
+    }
+
+    virtual void RunEntity(Entity entity, Components&... components) = 0;
+  };
+}