Adding support for custom background images

This change adds support for custom background images.

Usage:
- Background images are stored in "backgrounds" folder as with jpg or png.
- Both 360 degree (equirectangular) and 6-side cubemap images are supported. This is automatically detected based on aspect ratio (with cubemap having 4:3 aspect ratio).
- Select the background from Settings.

Changes:
- The selected background image is persisted in config in this format: "background": "backgrounds/my_background.jpg",
- Image is decoded in a background thread (via Android plugin), as Texture2D.LoadImage can cause multi-second freeze on the UI thread. We then compensate for unity (re-ordering coordinate origin and also alpha channel).
- Made ground smaller & semi-transparent

Assets/Scripts/SettingsHandler.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.IO;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.SceneManagement;
@@ -21,7 +22,9 @@ namespace QuestAppLauncher
         public GameObject gridPopulation;
         public GameObject show2DToggle;
         public GameObject autoUpdateToggle;
+        public GameObject skyBoxButton;
         public DownloadStatusIndicator downloadStatusIndicator;
+        public SkyboxHandler skyboxHandler;
 
         public Toggle tabsAutoOff;
         public Toggle tabsAutoTop;
@@ -57,6 +60,9 @@ namespace QuestAppLauncher
             // Load config
             this.config = ConfigPersistence.LoadConfig();
 
+            // Skybox callback
+            this.skyboxHandler.OnSkyboxSelected = OnSkyboxSelected;
+
             // Set current cols & rows
             var colsSlider = this.gridCols.GetComponent<Slider>();
             colsSlider.value = this.config.gridSize.cols;
@@ -75,6 +81,9 @@ namespace QuestAppLauncher
             // Set 2D toggle
             this.show2DToggle.GetComponent<Toggle>().SetIsOnWithoutNotify(this.config.show2D);
 
+            // Set skybox button text
+            this.skyBoxButton.GetComponentInChildren<TextMeshProUGUI>().text = SkyboxHandler.GetSkyboxNameFromPath(this.config.background);
+
             // Set auto-update toggle
             this.autoUpdateToggle.GetComponent<Toggle>().SetIsOnWithoutNotify(this.config.autoUpdate);
 
@@ -142,6 +151,19 @@ namespace QuestAppLauncher
             }
         }
 
+        public void OnSkyboxSelected(string skyboxPath)
+        {
+            // Update text
+            this.skyBoxButton.GetComponentInChildren<TextMeshProUGUI>().text = SkyboxHandler.GetSkyboxNameFromPath(skyboxPath);
+
+            // Save config with new skybox selection
+            if (!this.config.background.Equals(skyboxPath, StringComparison.OrdinalIgnoreCase))
+            {
+                this.config.background = skyboxPath;
+                ConfigPersistence.SaveConfig(this.config);
+            }
+        }
+
         public void DeleteRenameFiles()
         {
             Debug.Log("Delete Rename files");
@@ -166,6 +188,11 @@ namespace QuestAppLauncher
             rowsText.text = string.Format("{0} Rows", rows);
         }
 
+        public void ShowSkyboxList()
+        {
+            this.skyboxHandler.ShowList();
+        }
+
         private bool HasUsageStatsPermissions()
         {
             // Check if we have UsageStats permission