Revise the implementation of model-view transforms.

[pixelzoom]

This sim has some interesting model-view transform requirements, related to the zoom feature:

• Most things (lens, mirror, object, light source, rays, image, screen,...) are supposed to scale as you zoom in/out.
  *Labels are supposed to translate, but not scale.
• Rulers change model length so that their view length remains constant.

The above requirements are implemented via 3 different (but related) transforms, all defined in GOScreenView.js:

• modelViewTransform: ModelViewTransform2
• zoomTransformProperty: DerivedProperty< ModelViewTransform2 >
• zoomScaleProperty: DerivedProperty<number>

Having 3 transforms creates a few problem:

• Complexity - it's hard to keep track of what's going on.
• Ordering - The fact that zoomTransformProperty and zoomScaleProperty are dynamic (and both derived from zoomLevelProperty) is causing ordering dependencies, resulting in problems like (defintely) Incorrect ruler length with shuffleListeners query parameter #133 and (maybe) Inaccurate rendering with shuffleListeners query parameter #145.
• PhET-iO - more stuff to instrument, more stuff to explain to the instructional designer, ...

I'm fairly certain that the requirements can be met with a single Property<ModelViewTransform2>, and I'll be investigating that.

[pixelzoom]

The model-view transform was significantly simplified in the above commit. Tested with ?debugModelBounds to verify that the model bounds are behaving correctly.

[pixelzoom]

Reopening. This broken a bunch of things.

[pixelzoom]

Status:
#291 and #298 have been fixed.
#299 (rulers jump around) is still a problem.

[pixelzoom]

#299 was broken before these changes, as demonstrated in 1.1.0-dev.14. So closing this issue.