Use only one decimal place in StopwatchNode display

[arouinfar]

In https://github.com/phetsims/scenery-phet/issues/565 StopwatchNode gained the option of having only 1 decimal place in the readout. Since the StepForwardButton increment is 0.2s, the StopwatchNode doesn't need more than 1 decimal place.

@Denz1994 please update the StopwatchNode display to have only one decimal place.

[arouinfar]

See https://github.com/phetsims/scenery-phet/issues/617 for further discussion of StopwatchNode precision.

[samreid]

StopwatchNode number of decimal places options are discussed in https://github.com/phetsims/scenery-phet/issues/618

[Denz1994]

After changes in https://github.com/phetsims/scenery-phet/issues/618 it was fairly easy to use only one decimal place.

As a side note here are some changes I would make to the implementation of StopWatch in CLB:

• [x] timer in VoltmeterToolboxPanel.js should be refactored to reflect that it is just used as a placeholder. Maybe psuedoStopWatch or StopWatchImage.
• [x] CapacitanceScreenView.js doesn't need a stopwatch at all because it isn't on that screen.
• [x] VoltmeterToolboxPanel.js should be a ToolboxPanel.js because it doesn't just include the voltmeter anymore.
• [x] dragBounds is not used in VoltmeterToolboxPanel.js. Remove it.

[jonathanolson]

Completed.