[Feature Request] Manually marking a Table of Contents page

[lamaqdahodwala]

Recently, I've been downloading many books in PDF form, and the Table of Contents page is not being picked up by Thorium. My hypothesis for why this is happening is that the Table of Contents page may be in a different location than Thorium expects, and so upon searching for a TOC, it doesn't find anything.

My solution to this problem is to add a feature to manually designate a page as the Table of Contents. Users can click a button and set a page number (or range) where the TOC can be found, and then the preexisting TOC parser can take over.