The deadline daemon is supposed to send emails
to users who have borrowed books and are supposed to deliver
them back, or users who have added themselves to the queue,
and is waiting for a book.
- Create a common argument interface and config file format for both
cli and flask version of application.
- Bumped the python version constraint to ^3.11 in order to use the
native tomllib for reading config file.
- Move all the flask specific code under `worblehat.flaskapp`
