Implements automatic saving of notes. Issue #40

This is disabled by default and is saved within each browser as localStorage.
Always you can cancel the edit with Esc key.

On the other hand, now also allows you save the notes with Crl+Enter key, which
is more standard.

css/style.scss

@@ -226,8 +226,8 @@ div[contenteditable="true"] {
     border: none;
 }
 
-.note-options,
-.note-disable-options {
+.note-editable-options,
+.note-noneditable-options {
     padding: 8px;
     padding-top: 0px;
 }