feat: user shelf, authorization, refactoring, tests

[abinba]

Sorry for huge PR :(

!!! DO NOT MERGE !!!

UNTIL Flutter frontend is adjusted to use new auth and listening part is adjusted.

• Added validation for username, password, email
• Changed the auth logic to use JWT token
• Removed unnecessary endpoints
• Added search functionality
• Added shelf functionality
• Fixed Listening endpoints to better use
• 'first_chapter_id' added to Audiobook (you would need to specify it after creating the chapter OR use a database trigger :) )
• Unit tests added for endpoints (we now have 67% coverage xd)

Pay attention that the way to get audiobook chapters and see the info of 'Listening' of user has changed.

Now before you press play, you should first get audiobook chapters (/api/v1/chapters/<audiobook_id>) and see if there is a listening record (/api/v1/listening/?audiobook_id=1&account_id=1).

If there is, you just use the current_chapter_id.
If not, you should send a POST request to create it and just use the audiobook's first_chapter_id to start playing audiobook.
When you want to change the current_chapter_id, you send a PUT request.

There's no such thing now as explored chapters for now.

Well, no one cares I guess already anyway xD