Refactor to allow adding chhands/pauris in a different order

[dsomel21]

This is going to be a pretty big refactor, but it shouldn't be too complex.

• Right now, adding chhand only adds to the last book, last chapter.
• Adding a pauri, will automatically add it to the last book, last chapter, last chhand and so fourth.

We have to break this by allowing chapter_id or book_id arguments so we can add it wherever we want.