Improve stopwatch

[Riksu9000]

Cleaned up the messy code.
While the stopwatch is running, sleep is disabled.
While the stopwatch is running, the button will stop the timer. In all other cases the button will exit the app.
Fixes #379?

EDIT: Forgot to mention that removing the Events code also improves the responsiveness of the app, since it no longer waits for a screen refresh cycle.

[Avamander]

Did you run Clang-Format on the new code? I'm also not sure getting rid of the state machine made the functionality clearer.

[Riksu9000]

The state machine was inside the Refresh loop, which means it kept setting eveything multiple times per second. Now changes are made only when a button is pressed, and I think it is much easier to see what pressing a button does, whereas before some of the changes were in the button function, and some somewhere in the state machine.

Clang-format changes some lines so I'll commit that soon.

[ObiKeahloa]

Seems to be using an older base?

[JF002]

Looks good to me !
I agree with @Riksu9000 : The new code update what needs to be updated on response to an event instead of refreshing everything on each call to Refresh().