Move all core types into namespaces (#1886)

* Reorganize namespaces

- Most types are now moved into the `melonDS` namespace
- Only good chance to do this for a while, since a big refactor is next

* Fix the build

src/frontend/qt_sdl/ROMInfoDialog.h

@@ -69,7 +69,7 @@ private:
 
     QImage iconImage;
     QTimeLine* iconTimeline;
-    u32 animatedIconData[64][32*32] = {0};
+    melonDS::u32 animatedIconData[64][32*32] = {0};
     std::vector<QPixmap> animatedIconImages;
     std::vector<int> animatedSequence;
 };