Copy Note to clipboard when it cannot be saved

Also avoid showing the actual exception. It's not very useful to the
user, and we're logging the exception to Sentry anyway.

Related to #124

assets/langs/en.yaml

@@ -62,7 +62,9 @@ editors:
     addImage: Add Image from Gallery
     editFileName: Edit File Name
     tags: Edit Tags
-    saveNoteFailed: Failed to Save Note
+    saveNoteFailed:
+      title: Failed to Save Note
+      message: We're sorry, but we cannot seem to save the Note. It has been copied to the clipboard to avoid data loss.
 pro: Pro
 actions:
   newNote: New Note

lib/core/note.dart

@@ -303,6 +303,10 @@ class Note with NotesNotifier {
     await file.writeAsString(contents);
   }
 
+  String serialize() {
+    return _serializer.encode(data);
+  }
+
   // FIXME: What about error handling?
   Future<void> remove() async {
     assert(_filePath != null);

lib/screens/note_editor.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 import 'package:easy_localization/easy_localization.dart';
 import 'package:flutter/material.dart';
 import 'package:collection/collection.dart';
+import 'package:flutter/services.dart';
 
 import 'package:gitjournal/core/note.dart';
 import 'package:gitjournal/core/md_yaml_doc.dart';
@@ -331,11 +332,12 @@ class NoteEditorState extends State<NoteEditor> {
           : await stateContainer.updateNote(note);
     } catch (e, stackTrace) {
       logException(e, stackTrace);
+      Clipboard.setData(ClipboardData(text: note.serialize()));
 
       await showAlertDialog(
         context,
-        tr("editors.common.saveNoteFailed"),
-        e.toString(),
+        tr("editors.common.saveNoteFailed.title"),
+        tr("editors.common.saveNoteFailed.message"),
       );
       return false;
     }