Stopwatch improvements

[MaWalla]

When using the stopwatch app for an "extended" amount of time, e.g. 1-2 minutes and wanting to do more accurate measurements there by hitting the stop button in time, its annoying to have the display turn off at its set timeout, meaning it needs to be turned on again first. So I'd suggest to just keep the display on while the app is in use, perhaps dimming it to the lowest brightness setting instead of turning off after the timeout.

Then, despite being in conflict with #303, it would be nice to repurpose the physical button to stop the measurement (and once stopped, use it to exit the app again), since its kinda impossible to use the stopwatch for diving for example (to see how long one can hold their breath). To solve this conflict, it may be a good idea to make the button behaviour a setting (either use the button to stop the running measurement, or use the button to exit the app while the measurement goes on).
To get back to the diving example, starting a new measurement with wet display and hands is another problem, but maybe someone has an idea regarding this .