DropDownMenuBuilder needs more methods like DropDownBuilder<TModel>

[johnwc]

We need to be able to build the menu like we are able to with DropDown(""), but with standalone dropdown menu like so.

@Html.Bootstrap().DropDownMenu().MenuItems(m =>
{
    m.Link("Refresh", Url.RouteUrl("Refresh", new { id = Model.Id, name = Model.Name })).PrependIcon("fa fa-refresh").Tooltip("My tooltip.");
    m.Divider();
    ....
})

It would also be great if there was a RouteLink along side the Link method.

public BootstrapLink<TModel> RouteLink(string linkText, string routeName, object routeValues)