If a book is already checked out, let me add myself to a waiting list

As a dwyler
Once I have found a book that is in the library and I would like to borrow, but it is already checked out, I would like to be able to add myself to the queue for this book,
So that the dwyler who has the book knows that someone else would like to read it.

## Acceptance criteria

+ I can click a button to add myself to the queue for a book that I have searched for and is already checked out
+ Display the name of the user who currently has the book
+ The user who currently has that book gets an email to say someone is waiting for the book
+ The number of people in the queue is displayed on the book page