feat: use mod metadata for getting mod information

For now this doesn't mean much, but it will help when we need data
exclusive from the metadata, such as addon id and mod provider.

Also removes the metadata when the mod is deleted, and make the Mod.h
file a little more pleasing to look at :)

launcher/minecraft/mod/ModFolderLoadTask.h

@@ -19,11 +19,11 @@ public:
     }
 
 public:
-    ModFolderLoadTask(QDir dir);
+    ModFolderLoadTask(QDir& mods_dir, QDir& index_dir);
     void run();
 signals:
     void succeeded();
 private:
-    QDir m_dir;
+    QDir& m_mods_dir, m_index_dir;
     ResultPtr m_result;
 };