Re-add “old” JS variables

[Palloxin]

Describe your suggested feature

These:

They were comfortable to use, they do not work anymore. Currently the alternative for ChapterName is reader.chapter.name I have no idea what the others are.

Other details

No response

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open or closed issue.
• [X] I have written a short but informative title.
• [X] If this is an issue with a source, I should be opening an issue in the sources repository.
• [X] I have updated the app to version 2.0.0.
• [X] I will fill out all of the requested information in this form.