Do not show Tag Editing screen if the Note cannot have metadata

In the case of '.txt' notes or markdown notes without a yaml header.

lib/editors/common.dart

@@ -103,6 +103,7 @@ class EditorBottomBar extends StatelessWidget {
   final bool allowEdits;
   final bool zenMode;
   final Func0<void> onZenModeChanged;
+  final bool metaDataEditable;
 
   EditorBottomBar({
     @required this.editor,
@@ -111,6 +112,7 @@ class EditorBottomBar extends StatelessWidget {
     @required this.allowEdits,
     @required this.zenMode,
     @required this.onZenModeChanged,
+    @required this.metaDataEditable,
   });
 
   @override
@@ -137,6 +139,7 @@ class EditorBottomBar extends StatelessWidget {
             editorState,
             zenMode,
             onZenModeChanged,
+            metaDataEditable,
           ),
           elevation: 0,
         );
@@ -236,6 +239,7 @@ Widget _buildBottomMenuSheet(
   EditorState editorState,
   bool zenModeEnabled,
   Func0<void> zenModeChanged,
+  bool metaDataEditable,
 ) {
   return Container(
     child: Column(
@@ -262,6 +266,7 @@ Widget _buildBottomMenuSheet(
             Share.share(note.body);
           },
         ),
+        if (metaDataEditable)
           ProOverlay(
             feature: Feature.tags,
             child: ListTile(

lib/editors/scaffold.dart

@@ -57,10 +57,8 @@ class _EditorScaffoldState extends State<EditorScaffold> {
       editingMode = true;
     }
 
-    if (editingMode == false) {
     note = widget.editorState.getNote();
   }
-  }
 
   @override
   void dispose() {
@@ -149,6 +147,7 @@ class _EditorScaffoldState extends State<EditorScaffold> {
                     }
                   });
                 },
+                metaDataEditable: note.canHaveMetadata,
               ),
             )
           ],