Reset encoding mode to default for codecs with dynamic modes list,

when settings become incompatible with the chosen mode.
E.g. for flac if -11 was selected and nonsubset modes are disabled,
-7 is chosen instead.

CUETools.Codecs/UserDefinedEncoderSettings.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.ComponentModel;
+
+namespace CUETools.Codecs
+{
+    public class UserDefinedEncoderSettings : AudioEncoderSettings
+    {
+        public UserDefinedEncoderSettings()
+            : base()
+        {
+        }
+
+        public string SupportedModes
+        {
+            get
+            {
+                return m_supported_modes;
+            }
+            set
+            {
+                m_supported_modes = value;
+            }
+        }
+
+        public string DefaultMode
+        {
+            get
+            {
+                return m_default_mode;
+            }
+            set
+            {
+                m_default_mode = value;
+            }
+        }
+    }
+}