implemented DPK resource archives.

known encryption keys for:
Inbou no Wakusei
Ryoshuu
Ryobaku ~Haitoku no Atelier~
Ryoshuu ~Jogakusei Choukyou~
Shirogane no Cal to Soukuu no Joou
Shiromiko
Shoujotachi no Saezuri
Yumemiru Tsuki no Lunalutia

ArcFormats/WidgetDPK.xaml.cs

@@ -0,0 +1,17 @@
+using System.Windows.Controls;
+
+namespace GameRes.Formats.GUI
+{
+    /// <summary>
+    /// Interaction logic for WidgetDPK.xaml
+    /// </summary>
+    public partial class WidgetDPK : Grid
+    {
+        public WidgetDPK ()
+        {
+            InitializeComponent ();
+            if (null == EncScheme.SelectedItem)
+                EncScheme.SelectedIndex = 0;
+        }
+    }
+}