title: Ionic v3: Group list by date/day
body: <p>In good old version 1 of Ionic I was able to build an event-list grouped by date like this:</p>
  
  <pre><code>&lt;ion-list ng-repeat="(key, value) in events| groupBy: 'event.date'"&gt;
  
    &lt;div class="item item-divider" ng-if="value"&gt;
      {{ ::key | event.date }}
    &lt;/div&gt;
  
    &lt;ion-item class="item" ng-repeat="event in value track by event.event.event_id"&gt;
      {{ ::event.event.title }}
    &lt;/ionic-item&gt;
  
  &lt;/ion-list&gt; 
  </code></pre>
  
  <p>While the events object looks like this (event #1 and #3 share the same date):</p>
  
  <pre><code>{
    "events": [
      {
        "id": 1,
        "date": "2017-12-26",
        "title": "First event"
      },
      {
        "id": 2,
        "date": "2017-12-30",
        "title": "Second event"
      },
      {
        "id": 3,
        "date": "2017-12-26",
        "title": "Third event"
      },
      {
        "id": 4,
        "date": "2017-12-31",
        "title": "Last event"
      }
    ]
  }
  </code></pre>
  
  <p>This gave me a list of events stored in the "event" object grouped by "event.date". So all events on the same date where grouped by an item-divider:</p>
  
  <pre><code>+--------------+
  + 2017-12-26   +
  +--------------+
  | First event  |
  | Third event  |
  +--------------+
  + 2017-12-26   +
  +--------------+
  | Second event |
  +--------------+
  + 2017-12-26   |
  +--------------+
  | Last event   |
  +--------------+
  </code></pre>
  
  <p>How to achieve this with Ionic v3?
  Any ideas?</p>