Integrate users and books

- new table userbook linking users and book
- moved rating to users book
- updated demo data and tests
- updated front to hide routes from non connected users

internal/model/book.go

@@ -6,5 +6,4 @@ type Book struct {
 	gorm.Model
 	Title  string `json:"title" gorm:"not null"`
 	Author string `json:"author"`
-	Rating int    `json:"rating"`
 }