Maze start improvements

Although the progress bar was cool, it's even cooler to watch the maze get built. In the hopes of delighting players while they wait for mazes to be generated, I've replaced the loading bar with a visualization of the maze being built.

There used to be a couple of animations to indicate the player start position and the maze's exit, but those animations didn't seem to fit with the rest of the game. The player can now watch the maze get built and there is a delay before the countdown timer starts, so the player can look at the maze before being partly covered momentarily by the countdown timer. The countdown timer is now centered on the screen instead of at the maze exit. Hopefully that makes the timer more obvious. I worry that the maze's exit is less obvious, though.

Happy mazing!