NavItem includes anchor attributes on the li tag

`{...this.props}` passes DOM attributes to the li tag incorrectly. setting `href` and `title` on the `<li/>` tag

I "fixed" this by turning on the harmony features in grunt-react, and using the spread operator which is the recommended path from React. We can just as easily do this manually.

* set the props to null explicitly `<li title={null}`
* include a simple `omit` util like `_.omit`

The issue is larger than just passing odd attributes, unlike `transferToProps` the spread operator also passes along `props.children` in _most_ cases i've seen, this doesn't have an adverse affect, but sometimes it causes [weird bugs](https://github.com/jquense/react-widgets/blob/6af683ebdc20aed2ce8b69fc5355bb092d530355/src/SelectList.jsx#L317) where passing it to both the component and as children causes the child to get rendered twice.