Feature - Add ability to cancel modal if user clicks outside of modal

Possibly utilize this article:
https://dev.to/margaretkrutikova/elm-dom-node-decoder-to-detect-click-outside-3ioh

No file or test is named in the issue. Start by reading the linked article and locating the modal's event-handling entry point in this Elm library. Done means a modal can be cancelled when the user clicks outside it, while clicks inside remain unaffected; add or run the relevant tests if the project provides them.

Written by the indexing model from the issue text.