Book manager: Add validation when creating a new part
As of right now, we can add a part even if we do not fill any of the fields in the screenshot below.
This visually doesn't create anything, but a new part is created in the database. This affect the move modal, as you will see an empty row where you can move book components in and as well the TOC will have an empty row for this part.
This might generate again issues #284 (closed) and #285 (closed)