Search: Check if filename matches

Fixes #95

We really need search highlighting to showcase why an item matched while
searching. Additionally, soon we may need to give the user control over
what all should be searched.

lib/widgets/note_search_delegate.dart

@@ -69,6 +69,9 @@ class NoteSearchDelegate extends SearchDelegate<Note> {
       if (note.title.toLowerCase().contains(q)) {
         return true;
       }
+      if (note.fileName.toLowerCase().contains(q)) {
+        return true;
+      }
       return note.body.toLowerCase().contains(q);
     }).toList();