CUERipper: Allow editing Metadata using F2

Editing Track Titles has been possible using F2. Add the same behavior
to the Metadata list. This is an additional possibility using the
keyboard instead of clicking.

- Add `listMetadata_KeyDown` event for key `F2`
- Add `listMetadata_PreviewKeyDown` event for `Enter`
  Hitting Enter after editing will move to the next Metadata item now,
  as in `listTracks`.
- Keys for navigation in CUERipper under Tracks or Meta:
  Moving: Cursor up, Cursor down
  Editing: F2, Enter, Ctrl+Tab, Ctrl+Shift+Tab, Esc

CUERipper/frmCUERipper.cs

@@ -1856,6 +1856,28 @@ private void bnComboBoxC2ErrorModeSetting_SelectedValueChanged(object sender, Ev
                 selectedDriveInfo.drive.DriveC2ErrorMode = (int)bnComboBoxC2ErrorModeSetting.SelectedItem;
             }
         }
+
+        private void listMetadata_KeyDown(object sender, KeyEventArgs e)
+        {
+            if (e.KeyCode == Keys.F2)
+            {
+                listMetadata.FocusedItem.BeginEdit();
+            }
+        }
+
+        private void listMetadata_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
+        {
+            if (e.KeyCode == Keys.Enter)
+            {
+                if (listMetadata.FocusedItem != null && listMetadata.FocusedItem.Index + 1 < listMetadata.Items.Count)// && e.Label != null)
+                {
+                    listMetadata.FocusedItem.Selected = false;
+                    listMetadata.FocusedItem = listMetadata.Items[listMetadata.FocusedItem.Index + 1];
+                    listMetadata.FocusedItem.Selected = true;
+                    listMetadata.FocusedItem.BeginEdit();
+                }
+            }
+        }
     }
 
     internal class BackgroundWorkerArtworkArgs