cache: moved disk settings to a separate dialog

This way the cache settings can be accessed in both ProjectProperties and
Preferences.

app/render/diskmanager.h

@@ -135,6 +135,9 @@ public:
 
   static QString GetDefaultDiskCachePath();
 
+  void ShowDiskCacheSettingsDialog(DiskCacheFolder* folder, QWidget* parent);
+  void ShowDiskCacheSettingsDialog(const QString& path, QWidget* parent);
+
 public slots:
   void Accessed(const QString& cache_folder, const QByteArray& hash);