Ensure same colours are used in connectivity widgets for populations as are taken from nml file & used for 3d cells

[pgleeson]

These would be better if colours matched:

@borismarin mentioned that this should be relatively easy to do with an update to the method for opening the widget and passing parameters for the population colours as additional arguments

[borismarin]

That should do the trick:

• [ ] add an attribute to the Connectivity widget model, called e.g. nodeColormap which will store a d3 colormap (described below), which can be set via an optional argument when creating an instance of the widget.
• [ ] refactor the relevant widget types (force, chord, hive, to take this colour scale into account instead of using a hardcoded one - notice the old TODO comment regarding this fact...)
• [ ] use the Geppetto API to build a population_name -> colour mapping
• [ ] from this mapping (which doesn't need to be built explicitly) construct a d3 ordinal colour scale whose domain contains the population names, and the range each one of the colours (RGB hex strings)
• [ ] when creating an instance of the widget (via console), pass the d3 ordinal scale constructed above to nodeColormap , as well as a nodeType callback which will output the parent population for each node (node -> population mapping).

[mattearnshaw]

working prototype (for chords so far) in progress at https://github.com/openworm/org.geppetto.frontend/tree/connectivity-colors

[borismarin]

@mattearnshaw @tarelli notice that I've suggested constructing the colormap at widget creation time, since ideally we shouldn't have NeuroML specific (1),(2) code in the widget.

[mattearnshaw]

• [x] add test coverage (casper)