Revert incorrect changes made in last refactor

- TagEditorDelegate is subclassed in https://github.com/metabrainz/picard/blob/f96d4cc2f03441876c11c6e6460b5d32f5405322/picard/ui/metadatabox.py#L193
- restore get_tag_name() method (revert 4d8bcc3)
- and use passed parent (reverting 6d820db)

picard/ui/edittagdialog.py

@@ -101,23 +101,23 @@ def createEditor(self, parent, option, index):
         if not index.isValid():
             return None
 
-        tag = self.parent().tag
-        editor = self._create_editor_based_on_tag_type(tag, option, index)
+        tag = self.get_tag_name(index)
+        editor = self._create_editor_based_on_tag_type(parent, tag, option, index)
         self._configure_editor_for_tag(editor, tag)
         return editor
 
-    def _create_editor_based_on_tag_type(self, tag, option, index):
+    def _create_editor_based_on_tag_type(self, parent, tag, option, index):
         """Create appropriate editor widget based on tag type.
 
         Args:
+            parent: Parent widget
             tag: Tag name
             option: Style options
             index: Model index
 
         Returns:
             QWidget subclass appropriate for editing the tag
         """
-        parent = self.parent()
         if tag.partition(':')[0] in MULTILINE_TAGS:
             editor = QtWidgets.QPlainTextEdit(parent)
             editor.setFrameStyle(editor.style().styleHint(
@@ -166,6 +166,9 @@ def _create_completer_for_tag(self, editor, tag):
             return COMPLETER_CONFIG[tag].create_completer(editor)
         return None
 
+    def get_tag_name(self, index):
+        return self.parent().tag
+
 
 class EditTagDialog(PicardDialog):
 
@@ -463,7 +466,9 @@ def value_edited(self, item):
         Args:
             item: The QListWidgetItem that was edited
         """
+        print(item)
         row = self.value_list.row(item)
+        print(row)
         value = item.text()
         if row == 0 and self.is_grouped:
             self.modified_tags[self.tag] = [value]