fix: clear questStepPanelList before adding panels from a new quest

Before this, we kept adding and adding more panels, making the iteration over steps slower and slower

src/main/java/com/questhelper/panel/QuestOverviewPanel.java

@@ -255,6 +255,7 @@ private JPanel makeDropdownPanel(JComboBox dropdown, String name)
 	public void addQuest(QuestHelper quest, boolean isActive)
 	{
 		currentQuest = quest;
+		questStepPanelList.clear();
 
 		List<PanelDetails> steps = quest.getPanels();
 		QuestStep currentStep;