Allow "data" key for module navigations

[mamhoff]

What is this pull request for?

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',
      }
    ]
  }
}

Screenshots (remove if none)

[tvdeyen]

This is great. Thanks. Regarding Turbolinks. I plan to remove Turbolinks from the admin soon. The future of the Alchemy admin is Vue and then Turbolinks is useless anyway.

But until then this is a good change for extensions like alchemy-solidus

A view spec would be great, though

[tvdeyen]

Awesome. Thanks 👏