Allow live data sources to configure supported actions

We need to extend the live data configuration with support for configuring the available actions. I propose to introduce something like this:

{
  ...
  "meta": {
    ...
    "actions": [
      {
        "id": "edit",
        "name": "Edit",
        "description": "Edit entry",
        "icon": {...},
        "allowProperty": "doc.hasedit",
        "urlProperty": "doc.edit_url"
      },
      ...
    ]
  }
}

This configuration can be controlled from the live data source, and can be customized from the live data macro. Moreover, the actions displayer will have a property expecting a list of actions ids representing the actions to display in the Actions column.