Add a timer

[unfinishedideas]

I like to practice certain things in increments. Having an on screen timer would be a good feature to add. Being able to keep the metronome running and reset the timer would also be useful.

AC

1. Create a timer display that resets whenever the metronome is started / stopped
2. Make selecting the timer reset it to zero to start counting again from 0 again while the metronome runs
3. Implement this resetting function into the bar count functionality too