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/api/mapper.go

@@ -9,6 +9,13 @@ func (b bookPostCreate) toBook() model.Book {
 	return model.Book{
 		Title:  b.Title,
 		Author: b.Author,
+	}
+}
+
+func fromUserBookDb(b *model.UserBook) bookUserGet {
+	return bookUserGet{
+		Title:  b.Book.Title,
+		Author: b.Book.Author,
 		Rating: b.Rating,
 	}
 }