LibDraw: Put all classes in the Gfx namespace

I started adding things to a Draw namespace, but it somehow felt really
wrong seeing Draw::Rect and Draw::Bitmap, etc. So instead, let's rename
the library to LibGfx. :^)

Libraries/LibGUI/GPainter.cpp

@@ -29,8 +29,8 @@
 #include <LibGUI/GWindow.h>
 
 namespace GUI {
-Painter::Painter(GraphicsBitmap& bitmap)
-    : ::Painter(bitmap)
+Painter::Painter(Gfx::Bitmap& bitmap)
+    : Gfx::Painter(bitmap)
 {
 }