Change how score is displayed based on game mode

[johneastman]

• When the game mode is "Precision Shot", display the score as a number
• When the game mode is "Quick Draw", display the score as a time
• Create reusable utility that takes a number of milliseconds and displays the time in a human-readable format (minutes:seconds:milliseconds). This will be used to display the:
  • current/running score
  • High scores
  • Final score on end-game screen

[johneastman]

Closing because #53 was updated to better describe these changes. I'll add any additional information from here to that task.