Standardise data schemas of events

[benfrancis]

The event description on the actionsEventsThing needs updating from:

    {
      name: 'virtualEvent',
      metadata: {
        description: 'An event from a virtual thing',
        type: 'number',
      },
    }

to:

    {
      name: 'virtualEvent',
      metadata: {
        description: 'An event from a virtual thing',
        data: {
          type: 'number'
        }
      },
    }

The event description on the alarm thing needs updating from:

   {
      name: 'alarmEvent',
      metadata: {
        description: 'An alarm event from a virtual thing',
        type: 'string',
        '@type': 'AlarmEvent',
        readOnly: true,
      },
    }

to

   {
      name: 'alarmEvent',
      metadata: {
        description: 'An alarm event from a virtual thing',
        data:
          {
            type: 'string'
          }
        '@type': 'AlarmEvent',
      },
    }

(Note that readOnly was not valid in the legacy Web Thing API, it is technically valid in the W3C TD spec if inside data but is meaningless since all events are read-only.)