Add (light/web) novel chapters

[dvaJi]

It should use the markdown editor instead uploading pages when you want to create a chapter (ChapterDetail), and downloads should export an .pdf file instead a .zip file.

Reader example: https://www.webnovel.com/book/8212987205006305/22047897407242688/Trial-Marriage-Husband%3A-Need-to-Work-Hard/The-Flash-Marriage-Wife