Allow more nesting of sub menus in the main navigation

Currently the main navigation supports nesting of sub menus up to 3 levels. Any nesting beyond this does not work. 
From the structure below, all sub menus under **Mobile App** will not be expanded when you click on **Mobile App**

```markup
+ Specifications
   + Functional
      + Mobile App
         - Sign up
         - Sign in
      + Single Sign On
   + Technical
```