Add Event system

- Add abstract Event class
- Add EventDispatcher
- Add Mouse, Key and Window Events

CopiumEngine/src/copium/event/WindowFocusEvent.cpp

@@ -0,0 +1,13 @@
+#include "copium/event/WindowFocusEvent.h"
+
+namespace Copium
+{
+  WindowFocusEvent::WindowFocusEvent(bool focused)
+    : Event{EventType::WindowFocus}, focused{focused}
+  {}
+
+  bool WindowFocusEvent::IsFocused() const
+  {
+    return focused;
+  }
+}