Permit adding specific classes to nodes & SVG lines

[smonsarr]

Currently certain aspects of nodes and lines can be modified such as background-color etc. When working with a web publication that supports theming, it is some times not acceptable to directly specify colours in the content of the page. Such aspects must be exclusively managed by CSS.

This change to jsmind adds two node data fields :

• nodeClassList : an array of strings that will be added to the classList object of the rendered jmnode
• lineClassList : SVG only - an array of strings that will be added to the classList object of the rendered SVG path

This allows the content to exclusively specify intent such as "important". How "important" is relayed to the user is managed exclusively in CSS.

In the following example each branch is assigned a nodeColor class (nodeColor_1, nodeColor_2, etc). The actual colors are managed by CSS theme:

In this example a node data looks like :

{
	"id": "gp0mlO8fTKjMkdlhaUwp6c",
	"topic": "Application : Documentaires, Biographies",
	"nodeClassList": ["nodeColor_1"],
	"lineClassList": ["lineColor_1"]
}

[hizzgdev]

Thanks @smonsarr , your PR looks great. And I have some thoughts about the idea:

1. we have to add nodeClassList and lineClassList to the nodes whose appearance we want to change?
2. If the answer to the previous Question is true, I think it just like merge styles into a style rule?
3. considering the HTML class is not applicable to Canvas graphing, I would like to suggest achieving it in another way.
   3.1. could we read the style rule and change the style of the leading line for Canvas?
4. why do we need a list of className?