* When playing as the Bird, the dive attack is able to destroy other
mobile doodads such as Azulians and Thieves.
* The Box has been made invulnerable so it can't be destroyed by Anvils
or player-controlled Birds.
* Bugfixes with pop-up modals:
* The quit game confirm modal doesn't appear if another modal is
already active on screen.
* The Escape key can dismiss Alert and Confirm modals.
* Add "Level" menu items to Play Mode to restart the level or retry from
the last checkpoint (in case of softlocks, etc.)