energy2d import: simplify deletion of unused structure

No need to test for presence of key in Ruby Hash
before deleting it.
update imports/energy2d/content from energy.concord.org

Update html pages and associated e2d models from content
in http://energy.concord.org/energy2d.

Updated e2d models used by content are now all in
e2d sub-directory:

  imports/energy2d/content/e2d

The following models were removed:

- eee-conduction1.e2d
- gable-solar.e2d
- intro1.e2d
- skillion-solar.e2d

The html pages are modified in the following ways
when imported:

1. stylesheet link re-written to:

  href="_assets/css/product-page.css"

2. applet archive reference re-written from:

  archive="energy2d-applet.jar"

to:

  archive="/jnlp/org/concord/energy2d/energy2d.jar"
imports/energy2d/models-xml: 45 new, 52 updated

Also process all e2d files with xmllint, 2-space indentation

$ find inport/energy2d -name '*.e2d' | xargs -I % xmllint --format % --output %

new e2d models:

  barrel.e2d
  bolometer.e2d
  cable.e2d
  conservation-of-energy.e2d
  countercurrent-exchange.e2d
  cross-section-venturi.e2d
  double-bell.e2d
  double-bell2.e2d
  field-of-bar.e2d
  fin1.e2d
  ghosting.e2d
  hand.e2d
  kelvin-helmholtz.e2d
  man.e2d
  mantle.e2d
  natural-daylighting.e2d
  no-ghosting.e2d
  quadrupole.e2d
  rectangular-vs-circular-heat-source.e2d
  shelter.e2d
  solar-chimney.e2d
  solar-cycles-shadow.e2d
  solar-cycles.e2d
  solar-oven.e2d
  solar-oven2.e2d
  solar-updraft-tower.e2d
  solar-updraft-tower2.e2d
  solar-updraft-tower3.e2d
  spoon.e2d
  stack-effect.e2d
  step1.e2d
  step2.e2d
  thermal-bridge.e2d
  thermoregulation.e2d
  thermostat-cooling.e2d
  thermostat.e2d
  thermostat1.e2d
  thermostat2.e2d
  touch-convect.e2d
  touch.e2d
  trombe-wall-closeup.e2d
  trombe-wall.e2d
  usa-isotherm.e2d
  village1.e2d
  zeroth.e2d
e2d: convert environment, controller to null elements

The serialization into XML by Java E2D creates <environment> and <controller> elements with newlines.

This fix removes the newlines.
energy2d: importedFrom uses new e2d model location
update generated energy2d models and interactive

  $ ./imports/energy2d/convert-to-json.rb