Save when exit

1. fix image cache
2. fix save when exit since destructor won't be called
3. fix #583 #582 (partially)  #581 (partially)  #580

Wox.Infrastructure/Image/ImageLoader.cs

@@ -9,6 +9,7 @@ using System.Windows;
 using System.Windows.Interop;
 using System.Windows.Media;
 using System.Windows.Media.Imaging;
+using Wox.Infrastructure.Logger;
 using Wox.Infrastructure.Storage;
 
 namespace Wox.Infrastructure.Image
@@ -71,7 +72,7 @@ namespace Wox.Infrastructure.Image
 
         public static void PreloadImages()
         {
-            Stopwatch.Debug($"Preload {_cache.TopUsedImages.Count} images", () =>
+            Stopwatch.Debug("Preload images from cache", () =>
             {
                 _cache.TopUsedImages.AsParallel().Where(i => !_imageSources.ContainsKey(i.Key)).ForAll(i =>
                  {
@@ -87,6 +88,7 @@ namespace Wox.Infrastructure.Image
                      }
                  });
             });
+            Log.Info($"Preload {_cache.TopUsedImages.Count} images from cache");
         }
 
         public static ImageSource Load(string path, bool addToCache = true)

Wox.Infrastructure/Storage/ISavable.cs

@@ -0,0 +1,11 @@
+namespace Wox.Infrastructure.Storage
+{
+    /// <summary>
+    /// Save plugin settings/cache, 
+    /// todo should be merged into a abstract class intead of seperate interface
+    /// </summary>
+    public interface ISavable
+    {
+        void Save();
+    }
+}

Wox.Infrastructure/Wox.Infrastructure.csproj

@@ -78,6 +78,7 @@
     <Compile Include="Image\ImageCache.cs" />
     <Compile Include="Image\ImageLoader.cs" />
     <Compile Include="Logger\Log.cs" />
+    <Compile Include="Storage\ISavable.cs" />
     <Compile Include="Storage\PluginSettingsStorage.cs" />
     <Compile Include="Storage\Storage.cs" />
     <Compile Include="Stopwatch.cs" />