Display the number of notes in the listing

### What

A way to quantify the notes.

### Why

Sometimes it is useful to know how many notes are available to be listed.
As an example. I am migrating my notes from the Evernote to the Simplenote but I don't know how many notes I have already migrated. The Evernote already has this functionality and it displays in the top of the notes listing, the number of notes that are been displayed.

### How

Maybe display it in the header of the listing of notes?


Start by locating the notes-listing and its header in the repository, then trace the note data already used to render the list. Add a visible count in that listing header and verify that it reflects the notes currently available or displayed, including an empty listing.

Written by the indexing model from the issue text.