Make Lib.nestedProperty an npm module of its own

[etpinard]

So that users and plotly.js consumer projects can use it!

The tricky part will be to factor out the core nested property logic from the plotly.js-specific parts (namely plot_api/container_array_match.js).

Wrapping nestedProperty in a constructor should do the trick. For example, plotly.js/src/lib/nested_property.js could become:

var NestedProperty = require('@plotly/nested-property');
var containerArrayMatch = require('../plot_api/container_array_match');

module.exports = new NestedProperty({containerArrayMatch: containerArrayMatch});

cc @bpostlethwaite @alexcjohnson

[alexcjohnson]

@etpinard sounds great! The only change I'd suggest is instead of containerArrayMatch, factor out isDeletable - there's more plotly.js-specific logic in there than just containerArrayMatch. That said, this logic is fairly obtuse and always makes me wonder how much would really be lost if we ditched it or at least simplified it...

[etpinard]

Probably not going to happen in the near future. Closing.