Battery voltage display and holeshot timing

[odddollar]

Added:

• Battery voltage display to configuration page. Based off code from Feature/fastestlap and show battery voltage #17
  
• Holeshot timing. Time taken between race start and first lap being initiated (known as "holeshot") is displayed on the race page, with corresponding voice callouts
• Clicking Stop Race now resets race internally, allowing for starting a new race with a new holeshot without clearing the display of previous laps/races
  
• "Starting race in less than 5" now takes a random amount of time up to 5 seconds to start

This pull request is a fix for #23, which had a horrible commit history. This has the same changes but has a nicer history.

[odddollar]

@phobos- Wondering if you could take a look at my changes and approve them?

[phobos-]

Apologies for the late reply. Tested on my unit, looks good 👍