Support actions in tour

[mirkobrombin]

In this commit I added a prototype of action based on prefixes.

    {
        "resource": "/org/vanillaos/Tour/assets/configure.svg",
        "title": "Configure Your Device",
        "description": "From Bluetooth devices to that wallpaper you love so much. The settings panel allows you to configure it as you like.",
        "hasAction": true,
        "action": {
            "title": "Open the Settings",
            "callback": "cmd://gnome-control-center"
        }
    }

The following explain each key:

• hasAction is a boolean, this could be removed if we check for the presence of the action key instead
• action contains the metadata for the action:
  • title is the name of the action which will be displayed in the button
  • callback is the one containing the real action, the idea is to define each action using a prefix to inform the backend how to process them:
    • cmd:// where the remaining characters is the command to launch
    • url:// where the remaining characters is the url to open in the web browser

this is just a prototype, the whole structure can be changed/improved. There is no backend that manages it.