[reserved] Library CRUD

[lzrmihnea]

Create backend submodule for online library books management

• NoSQL representation of user-book relationship
• Create basic JSON diagram of nosql representation with basic representation of book
• Assume relevant fields, using current task description
• Create new book
• Borrow book
• Return book
• Delete book
• Update state of book
• Check how many issues are available for a certain book and if a student/professor can borrow a book
• Optional: daily check if borrowed book has been borrowed for more than 2 weeks