Pointer areas sign-off

[pixelzoom]

For #262.

We'll need to get this from @amanda-phet before QA testing begins (3/20).

I think we're in good shape here, but I'll have a look before assigning to @amanda-phet.

[pixelzoom]

@amanda-phet this is ready for review.

Note that there's one place where touch areas overlap a bit -- when the reference line scrubber and area scrubber (or tangent scrubber) are at the same x location. See screenshot below. We feel that this is acceptable.

[amanda-phet]

Pointer areas look good to me.