Remove the title editor if it cannot be stored

It just makes it confusing for the user otherwise.

lib/editors/checklist_editor.dart

@@ -124,7 +124,7 @@ class ChecklistEditorState extends State<ChecklistEditor>
       floatingActionButton: buildFAB(widget, this),
       body: Column(
         children: <Widget>[
-          titleEditor,
+          if (widget.note.canHaveMetadata) titleEditor,
           Expanded(child: FocusScope(child: checklistWidget)),
         ],
       ),

lib/editors/markdown_editor.dart

@@ -66,7 +66,7 @@ class MarkdownEditorState extends State<MarkdownEditor> implements EditorState {
       child: SingleChildScrollView(
         child: Column(
           children: <Widget>[
-            _NoteTitleEditor(_titleTextController),
+            if (note.canHaveMetadata) _NoteTitleEditor(_titleTextController),
             _NoteBodyEditor(
               _textController,
               autofocus: widget.autofocusOnEditor,

lib/widgets/note_viewer.dart

@@ -47,7 +47,7 @@ class NoteViewer extends StatelessWidget {
         children: <Widget>[
           if (note.created != null && showJournalHeader)
             JournalEditorHeader(note),
-          if (showTitle)
+          if (showTitle && note.canHaveMetadata)
             NoteTitleHeader(note.title),
           Padding(
             padding: const EdgeInsets.only(top: 8.0, bottom: 8.0),