Added hold block and minor fixes

src/states/State.h

@@ -43,6 +43,7 @@ struct StateContext {
     SDL_Texture* scorePanelTex = nullptr;
     SDL_Texture* statisticsPanelTex = nullptr;
     SDL_Texture* nextPanelTex = nullptr;
+    SDL_Texture* holdPanelTex = nullptr; // Background for the HOLD preview
     SDL_Texture* mainScreenTex = nullptr;
     int mainScreenW = 0;
     int mainScreenH = 0;