[SDK-721] Add clearing of panel switcher (#194)

## [SDK-721](https://ready-player-me.atlassian.net/browse/SDK-721)

## Description

- Added clear functionality in panel switcher, which will be called on OnDestroy

Author: rYuuk

Samples~/AvatarCreatorSamples/LegacyAvatarCreator/Scripts/UI/CategoryUICreator.cs

@@ -48,6 +48,11 @@ private void OnDisable()
             outfitCategoryButton.RemoveListener();
         }
 
+        private void OnDestroy()
+        {
+            PanelSwitcher.Clear();
+        }
+
         private void Initialize()
         {
             categoryButtonsMap = new Dictionary<AssetType, CategoryButton>();

Samples~/AvatarCreatorSamples/LegacyAvatarCreator/Scripts/UI/PanelSwitcher.cs

@@ -64,6 +64,11 @@ public static void Switch(AssetType category)
             }
         }
 
+        public static void Clear()
+        {
+            CategoryPanelMap?.Clear();
+        }  
+      
         private static void DisableAllPanels()
         {
             foreach (var panels in CategoryPanelMap)