QoL and Control Updates

QoL Updates:

• Fixed 1-Up so that it doesn't continue falling when the game is paused
• Made the "game-over" screen properly display high score
• Made the "game-over" screen display previous high score if player achieves new high score
• Fixed invulnerability flashing animation

Controls updates:

• Added reverse thrust
• Added ability to shoot with spacebar
• Added strafing with "A" and "D"
• Added ability to flip direction ship is facing with "W" and "S"