Send model events to google analytics
boiling point fixes - neutral barrier color and max temp 700K

[#46685069]
added subtitle and about to pendulum interactive

[#47294585]
Make slider handle more 3d, darken inner line

[#46375547]
gh-pages.sh: stop if guard running, download tarball
Merge pull request #23 from concord-consortium/wip_interactive_gac

Send model events to google analytics
Setup onClick handlers again after repaint operation

[#47350021]
Position slider labels in a more general way
Position slider and slider handle when it has custom height
Divide atomsWithin() into atomsWithinRect() and atomsWithinCircle()

[#47185091]

1. To be consistent with atomsWithinTriangle().
2. All these functions takes a lot arguments. For possible readers
   (note it's scripting API), it would extremely difficult to assess
   which function call describes which shape.
Update tests of atomsWithinTriangle() function

[#47185091]
Support 'secondValue' property in bar graph

[#46397093]

It lets author display any additional value using small triangle.
Support "secondProperty" binding in bar graph controller

[#46397093]
Present bar graph, which is bound to two properties (one is average)

[#46397093]
Provide default values for filtered output 'type' and 'period'

These values are used across most of the interactives so use them as
default.
Support 'displayAverage' option in bar graph controller

[#46397093]

This option is for authors convenience. It causes that filtered output
is automatically defined (it uses basic property as an input). Author
doesn't have to define it manually.
Update bar graph interactive to present 'displayAverage' option

[#46397093]
Start model each time dye is dropped in "Dropping Dye on Click"

[#47350021]

Also, don't start model automatically, as Safari bug is now fixed.
move constants to common

Constants will be used for multiple model types

But for now to work with this script:

  ./node-bin/convert-mml-files

This move requires a symbolic link in:

  md2d/models/engines
Use dataGamesProxyPrefix for Netlogo exporter