Swap lower and higher buttons in pressure equilibrium interactive

[#51984107]
corrected program invocation comment
initial draft of harvesting light for photosynthesis interactive
scaleable photon key in blackbody interactive
better indication of photon key in greenhouse gas interactive
initial draft of absorption spectroscopy interactive
initial draft of emission spectroscopy interactive
move 2 MD2D models to ./models dir

When models are in effect created/maintained by hand
they should go in this directory: src/models/md2d

The only JSON files in src/interactives should be
Interactive JSON files.
more descriptive name for empty diffusion Interactive
remove incorrect type attributes in model refs
interactive migration: add type to model references

This is just a very first early hack to run a migration
changing the schema for Interactives.

Model references in Interactives now include a type attribute.

There are a number of useful reasons for apps that manage
Interactives to know about model types used in an Interactive
without having to load the model.

The next commit will include all the changed Interactives
and updates in the metadata.
updated all interactive model refs to include type

Interactive metadata and tests updated also
move css to block at top to support parallel loading
copy jquery.min.map to support better debugging
move main css after library css

So for example the overide of the default .Codemirror height
in interactives.css takes effect.
Snapshot phantomjs rack application created
Shapshot: phantomjs PNG service takes WxH  params

relative images are re-written (usually?)

Here the background image isn't rendered: http://screencast.com/t/5offHW8nfP
But here it is: http://screencast.com/t/QRl6QWwszFu
Shapshot phantom: Save html, use base_href, &  CSS

Instead of rewriting the html and css, we simply change the doc base.
We are saving both HTML and PNG files now, so that we can debug the html

Shapshot application.js: extract snapshot.js send css, send base_url

I removed the snapshot specific code out of application.js and into its
own javascript file.

Also: We now send all the stylesheets in the page, and a base url.
snapshot: interactives.html: Snapshots go to extra's area.

Also include snapshot.js
snapshot.js: phantomjs : Canvases ➙ data-url png's