Implement game start sequence

[wkeeling]

After pressing space bar on the landing page to start a new game, there is an animation sequence involving the ship.

[wkeeling]

Perhaps don't bother with the ship, but the start screen should display the different powerup types, and allow the player to start from round 1, or from a round that they choose.

[wkeeling]

Start screen has been implemented.

[wkeeling]

Re-opening issue to track the fact that the animation sequence involving the ship still needs implementing. Game landing page has been implemented however.