Allow "data" key for module navigations

This allows specifying a `data` key in module navigations. That way
one can add, for example, `data-turbolinks='false'` to a navigation entry.

In a module definition, it looks like this:

```
alchemy_module = {
  engine_name: 'spree',
  name: 'solidus',
  navigation: {
    controller: 'spree/admin/orders',
    action: 'index',
    name: 'Store',
    image: 'alchemy/solidus/alchemy_module_icon.png',
    data: { turbolinks: false },
    sub_navigation: [
      {
        controller: 'spree/admin/orders',
        action: 'index',
        name: 'Orders',
      }
    ]
  }
}
```

app/views/alchemy/admin/partials/_main_navigation_entry.html.erb

@@ -1,5 +1,5 @@
 <% if can? *navigate_module(navigation) %>
-  <%= content_tag :div, class: main_navigation_css_classes(navigation) do %>
+  <%= content_tag :div, class: main_navigation_css_classes(navigation), data: navigation["data"] do %>
     <%= link_to url_for_module(alchemy_module) do %>
       <% if navigation["image"] %>
         <%= image_tag(navigation["image"]) %>