Add option to prevent auto-navigation to top page of a nested group when expanding

[jfishman1]

When you add nested groups of pages in the navigation of docs.json, it will automatically navigate you to the top page of that group when you expand it on the left-hand nav.

For example:

{
   "tab": "Tab1",
      "groups": [
        {
          "group": "Group 1",
          "pages": [
            "docs/page1",
            {
              "group": "Group 2",
              "pages": [
                "docs/page2,
              ]
            },

If you click the "Group 2" drop down, it automatically navigates you to page docs/page2

Ideally, it would simply expand the group and not auto-navigate you to the page.