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. :^)

Applications/IRCClient/IRCWindowListModel.cpp

@@ -63,7 +63,7 @@ GUI::Model::ColumnMetadata IRCWindowListModel::column_metadata(int column) const
 {
     switch (column) {
     case Column::Name:
-        return { 70, TextAlignment::CenterLeft };
+        return { 70, Gfx::TextAlignment::CenterLeft };
     }
     ASSERT_NOT_REACHED();
 }