Actually add MainMenu class
Opening animation
Only show 'click to focus' message when embedded in a browser
Transitions into game
Visiting main menu should not clear data
Shortcut the intro bit
Show all unlocked levels when first seeing level select screen
Don't show all levels if not all unlocked
Skip intro sequence better
Menu will fade in from level select, not just first time
Better selected button appearance on main menu
Can cancel a transition from level select to level
Tween from level select to main menu
Handle pressing escape mid-transition main menu to level select
Make main menu selection persistent in a better way