'highlight' configuration values missing

[bryfox]

On the sociogram, Network Canvas will look for a highlight property and set the variable to its value.

Architect doesn't set value, so attributes won't be toggled.

• Architect should allow value configuration
• Architect needs to also allow configuring the value type (or document otherwise)?
• Should Architect default value to true?
• Should Network Canvas infer an undefined value to be truthy (since undefined results in a no-op)?

[wwqrd]

We did decide to only allow boolean variables here, which are only ever going to have a value of true. Making the value config is redundant. So perhaps we should remove it outright.

However, if we want to keep the flexibility of having a value prop, my feeling is that we shouldn't default in NC, as the variable type could be non-boolean.

[wwqrd]

Superseded by https://github.com/codaco/Network-Canvas/issues/710