Feature: Show page numbers visually

[ddfreiling]

A highly requested feature from our study-book users is being able to visually see the page numbers of the book.

Could this be made as a togglable feature? We'd love to give the implementation a shot, if EDRLab is onboard with having this feature in Thorium Reader.

Somewhat related to #1958

[gautierchomel]

This is related to discussion #1799, and #1951.

The main difficulty for a reading system is that forcing display of page numbers will result in strange patterns as they can be in the middle of a phrase or a word.

The best UX would probably be to have a margin display.

[danielweck]

Moved to discussion #1799 (comment)