Read-only support in edit view

[allantatter]

It would be good if readonly() method works in edit view. It should display the uploaded files but not show the buttons below to open media library or delete files.

https://nova.laravel.com/docs/2.0/resources/fields.html#readonly-fields

[KasparRosin]

@allantatter Maybe we should look into policies instead/also. https://nova.laravel.com/docs/3.0/resources/authorization.html#policies

Then we can define what exactly can the user do. We could build upon that to allow users to view only specific images or update only image metadata, but not upload new images.