set atom temperature scripting api and engine support

[#49515119]
gases in tube start at same temperature regardless of the side of the obstacle

[#49516635]
explain "volume" of planar gas in diffusion interactives

[#49658419]
distribute velocity from hot to cool atoms when setting temperature

[#49515119]
smaller key in diffusion interactive

[#47225527]
Fix drawing of xlabel and ylabel

[#49985163]
Add new controls to Viewport Demo interactive

[#49985163]
Optimize viewport changes, do not redraw the whole container

[#49985163]

It's enough to change viewBox attribute + redraw gridLines + units.
Atoms and interior of the model doesn't have to be changed.

Because of that, viewport changes can be really smooth now.
Fix workaround for requirejs isBrowser test

[#50029005]
Add promoter and terminator sequence to genetic engine

[#41020919]
Add definitions of nucleotides paths (reverse engineering of Fablevision images...)

[#41020919]

So, we won't have to use <image> tag, but create these elements by
hand. This will allow us to style them using CSS.
Add new nucleotides module, implemented as d3 reusable component

[#41020919]

I've completely refactored previous implementation and based this one
on approach used e.g. in d3.svg.axis() component.
Style nucleotides in various regions (coding, promoter, terminator)

[#41020919]
Major refactoring of genetic renderer (e.g. nucleotides module, viewport)

[#41020919] [#50058101] [#48761765]

Most important changes:
 - general cleanup (still some work to do),
 - new nucleotides module used,
 - viewport model options are always updated if genetic renderer
   modifies them.
Add viewport slider to "DNA Animations Example"

[#41020919]

So it's possible to take a look at promoter and terminator regions.
Fix / tweak how nucleotides change their direction before translation
Generate junk DNA sequence in genetic engine

[#49931937]
Render junk region at the beginning and at end of visible DNA

[#49931937]

Add new styles in .sass file.
Adjust viewport slider in "DNA Animations", so junk DNA can be reviewed

[#49931937]
Refactor genetic engine - support new intro states, simplify API

[#48666599]

Update Scripting API too.