USER STORY: Choose Category

[rhiannonmcn]

As a user I can choose the category for a book I upload so that the book is easily searchable

• [x] Create Susperuser
• [x] build admin panel to mange book listings & reviews
• [x] add Category, Book and BookReviews to admin.py
• [x] populate Category table with 7 main genres of books
• [x] Add prepopulated fields for the slug for Book table (to include title and author entries)
• [x] Add a sort filter for reviews and book listings to be sorted by created date or whether or not they are approved by admin

[rhiannonmcn]

• [x] Create category model