force backing_scale = 1 even when backingStoreRatio > 1

[#52558183]

Don't understand why this fixes the issue on Safari 6.0.5 on
Retina MacBook … but it does.
Energy2D: Fix rendering of invisible parts

[#52558183]

Use visibility: hidden to hide parts. When display: none is used,
positioning of labels fails and e.g. Firefox rendering fails
completely.
Energy2D: Rm backing_scale parameter from heatmap

[#52558183]

... to avoid confusion. We can safely rely on default browser
behavior, as now .getImageData(0, 0, W, H) always returns array with
W * H elements. One year ago we had to detect if we are not dealing
with Retina displays and do some hacks to ensure that we operate on
100 x 100 array.
Energy2D: Fix WebGL broken a few commits ago
Energy2D: Change style of WebGL status box

[#52401585]
Remove unnecessary rules and target builds from Makefile + cleanup

Now there is no sense to build MD2D, E2D, Sensor or Solar System, as
all of them would be exactly the same file... They are just Lab model
types and their public APIs references Interactives Controller (they
should be removed too).
Remove unnecessary public-api modules and RequireJS build configs
Export everything under Lab namespace

controllers.interactivesController -> Lab.InteractivesController
benchmark -> Lab.benchmark
Energy2D: Fix various bugs related to parts and sensors

Caused mainly by incorrect D3 data binding.
Gemfile: update shutterbug API
application.js & embeddable.html: new shutterbug API with iframe support
Energy2D: Simplify sensor and parts implementation
rack-livereload: use default value for min_delay

This should make no difference in operation, but it
does reduce the variables when investigating performance.

Also clarify use of environment in rack app.
rebuild top-level html files when config changes
Guardfile: also kickoff livereload w/JSON changes

Now changing the JSON for an Interactive should
reload the browser when in development mode and
running Guard.
Bump shutterbug to 0.0.9 to support multiple snapshot destinations.
Bump shutterbug to 0.0.9 to support multiple snapshot destinations.
Energy2D: Slightly change WebGL status styles

[#52401585]
Energy2D: Slightly change WebGL status styles

[#52401585]
Energy2D: Update WebGL status after use_WebGL option change

[#52401585]