Custom confirmation dialogs

[iamlogand]

Replace the confirm() function that is currently used to get the browser's default confirmation dialog (for game deletion) with a React component. This component could use MUI.

I would have proposed that the same component used for the sign out dialog should be used. However, that component was created "from scratch" before MUI was added to the app, so there is probably a much simpler way to make a dialog using MUI. Therefore, don't reuse the sign out dialog for this.

This component must be reusable. In the future, it would be great to implement it not only in the game lobby, but elsewhere in the app, including the play page.