[plug-in] Make it possible to render hyperlinks in the Tree node

[vitaliy-guliy]

For some plugin this feature may be required.
The main part will recognize that plugin provides a hyperlink and render it.
The markdown for hyperlinks may be looks like the markdown on GitHub.

Then if plugin provides following for the node label

{
    label: 'Anton Kosyakov [GitHub](https://github.com/akosyakov)'
}

then tree node in the main part will look like this

• Anton Kosyakov GitHub

Clicking on hyperlink must open new browser tab.

It could be great if tree-view-sample-plugin will use this feature.