Add breadth to book dimension

[ghostbear]

Describe your suggested feature

Currently, there is only width and height but it would be nice to also have breadth (thickness).

Other details

Would also be good for statistics later as it would allow for the calculation of the cubic volume of books one have

Acknowledgements

• [X] I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• [X] I have written a short but informative title.
• [X] I have updated the app to the latest version.
• [X] I filled out all of the requested information in this form.

[alessandrojean]

I thought about this later as well and will likely add at some point 👍🏻

[alessandrojean]

Closed in 119b05f.