CSS styling added when generating TOC (sigil_not_in_toc...)

What steps will reproduce the problem?

1. Create new epub file like below

     <body>
       <h1>Chapter h1</h1>
       <h2>Title h2</h2>
       <h2>Title h2</h2>
       <h3>Subtitle h3</h3>
     </body>

2. Click on Generate Table of Contents, from the list, 
   untick "Subtitle h3" and hit OK
3. Now when you toggle back to code view, you will notice 
   that sigil added few id's and classes to all h2 and h3

     <body>
       <h1>Chapter h1</h1>
       <h2 id="sigil_toc_id_1">Title h2</h2>
       <h2 id="sigil_toc_id_2">Title h2</h2>
       <h3 class="sigil_not_in_toc">Subtitle h3</h3>
     </body>

This is new behavior since last time I used sigil (few months
ago). Back then whenever I generated TOC it never added any 
CSS styling to the code. I hate having a messy code when I 
make my books, How do I turn it off?

Original issue reported on code.google.com by ds2...@gmail.com on 18 Nov 2014 at 11:24

oasegips / sigil

CSS styling added when generating TOC (sigil_not_in_toc...) #2501