Downsize MB is now user-configurable

Probably doesn't matter most of the time since we resize down HEIC and PNG anyway...

Closes #7

src/ViewModels/MainViewModel.cs

@@ -706,7 +706,7 @@ class MainViewModel : BaseViewModel, IFontResolver, ICanCheckShutdown
                     didAdjust = true;
                 }
                 // perform needed image manipulations
-                if (isHEIC || isWebp || isPNG || (!isPDF && info.Length > 1.5 * 1024 * 1024 /* 1.5 MB */))
+                if (isHEIC || isWebp || isPNG || (!isPDF && info.Length > _settings.ImageResizeThreshold * 1024 * 1024))
                 {
                     // Save image as jpg
                     mImage.Quality = 80;

src/ViewModels/SettingsViewModel.cs

@@ -87,6 +87,16 @@ class SettingsViewModel: ChangeNotifier
         }
     }
 
+    public decimal ImageResizeThreshold
+    {
+        get => _settings.ImageResizeThreshold;
+        set
+        {
+            _settings.ImageResizeThreshold = value;
+            NotifyPropertyChanged(nameof(ImageResizeThreshold));
+        }
+    }
+
     public async void ChooseOutputFolder()
     {
         var topLevel = _topLevelGrabber?.GetTopLevel();