feat(Vectorizer)!: support camel case attributes, add attributeNames static property

[kumilingus]

Description

The PR enables the camel case attribute support by default and makes the attributeNames property public.
The supportCamelCaseAttributes property remains private.

Before:

V('g').attr('myAttribute', 'value') // <g myAttribute="value"/>

Now:

V('g').attr('myAttribute', 'value') // <g my-attribute="value"/>

Allows you to use camel case attribute names anywhere in JointJS. e.g targetMarker, mvc.View.prototype.attributes

Migration guide

If you need any attribute to stay camel cased, you have to define it through attributeNames property.

V.attributeNames['myAttribute'] = 'myAttribute';
V('g').attr('myAttribute', 'value') // <g myAttribute="value"/>