Support per node styling

[GiantRobato]

Is your feature request related to a problem? Please describe.
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I'm using dependentree to visualize dependencies but sometimes a dependency fails. It would be helpful for me to color those dependencies separately from the other nodes.

Describe the solution you'd like
Add in the constructor a way to specify a field to look for if you want to override the default node color. Example:

// js
const tree = new DependenTree("div#tree", {
      overrideColorField : "_color"
    });


// json
[
    {
        "_name": "Component",
        "_deps": [
            "Extension 1",
            "Extension 2"
        ],
       "_color": "red"
    }
]

Describe alternatives you've considered
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Additional context
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