Add a new book to the library

[rody]

As an Library admin I want to be able to add a book to the library. The required fields are:

• Title
• ISBN (must be a valid 10 or 13 number ISBN)

Acceptance criterias

• [x] Admin can successfully add a new book
• [x] Non-admin cannot add a book
• [x] Can't have duplicate ISBN

[rody]

@rody don't forget to show that a non-admin user can't add a book

[rody]

related to #17