LibCore: Add CEvent and make LibGUI/GEvent inherit from it.

LibCore/CEvent.cpp

@@ -0,0 +1,12 @@
+#include <LibCore/CEvent.h>
+#include <LibGUI/GObject.h>
+
+CChildEvent::CChildEvent(Type type, GObject& child)
+    : CEvent(type)
+    , m_child(child.make_weak_ptr())
+{
+}
+
+CChildEvent::~CChildEvent()
+{
+}

LibCore/Makefile

@@ -1,7 +1,6 @@
 OBJS = \
-    CElapsedTimer.o
-
-LIBS =
+    CElapsedTimer.o \
+    CEvent.o
 
 LIBRARY = libcore.a
 STANDARD_FLAGS = -std=c++17 -Wno-sized-deallocation