Use Stopwatch and StopwatchNode

[samreid]

From phetsims/gas-properties#170: PENDULUM_LAB/StopwatchNode now has features supported in SCENERY_PHET, and should be updated accordingly.

I've made these changes and will reassign to responsible dev for review after pushing.

[samreid]

@jonathanolson can you please review at your convenience?

[jonathanolson]

Looks good, thanks!

[samreid]

There are still TODOs marked for this issue, discovered during phetsims/chipper#946

[samreid]

It looks like Pendulum lab has its own stopwatch. That should be deleted and the scenery-phet common code one should be used instead. Unassigning until we return focus to this sim.

[pixelzoom]

@samreid This issue is ready-for-review but unassigned. Should ready-for-review be removed?