Show stopwatch and timer time when on a different page

Otherwise there's no indication whatsoever that a timer or stopwatch is running.

For the stopwatch elapsed time is shown. For timers, in case of a single timer, its remaining time is shown, otherwise "n Timers".

TimerModel: Add running timers count property

In case there's more than one (cf. running timer property), we still might want to know about that.

Timer: Show hours in toPretty only when an hour has elapsed

Matches what the stopwatch does.

Move Stopwatch display to StopwatchTimer

Allows to use it outside StopwatchPage.

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