Dilate touch areas on charge NumberControls

[arouinfar]

For phetsims/qa#221

@kathy-phet commented that the charge controls were a bit tricky to use on mobile, and recommended dilating the touch areas a bit.

There's plenty of room, so I think something like this would be helpful @mbarlow12.

[kellywurtz]

On rc.6, looks like the slider touch area size increased, but not the arrows. Looking on Windows 10 Chrome.

[arouinfar]

Good catch @kellywurtz. @kathy-phet's original concern was more with the tweakers, so it'd be good to fix @mbarlow12.

[arouinfar]

Tagging phetsims/qa#235 so this issue shows up in the list.

@mbarlow12 I don't see any recent commits here, so not sure if #89 (comment) was addressed or not.

[kathy-phet]

phettest looks smaller than the above screenshot, so something looks like it was reverted. Do please increase both tweekers and thumb.

[kathy-phet]

The above was seen on phettest. Amy thought that perhaps the change Kelly saw was not done on master? @mbarlow12 - please make sure master has any of the fixes too.

[KatieWoe]

This looks good 1.0.0-rc.8