add testcases for when Simon should be start or stop listening to player clicks
implement when Simon start and stop listening to player clicks
add testcases for page states
implement page states

the page will either be in Simon's turn state, Player's turn state or Game over state
tiles :hover and :active will only be in effect during the player's turn

each state will reveal a message indicating whose turn it is (useful on mobile devices
where :hover isn't available)