title: Add a scale bar to a map
body: <p>Is it possible to add a scale bar to a map?</p>
  
  <p>I was hoping for something 'built in' like:</p>
  
  <pre><code>map.addControl(new mapboxgl.Scale({position: 'bottom-right'}));
  </code></pre>
  
  <p>Seems it was possible via a leaflet control in the classic js</p>
  
  <pre><code>L.control.scale().addTo(map);
  </code></pre>