title: How to show "parent data" of model on Grid?
body: <p>So I've a problem 'cause i want to show parent data on grid, illustrated here:</p>
  
  <p><strong>PARENT MODEL</strong></p>
  
  <pre><code>Ext.define('Ab.model.Marca', {
      extend: 'Ext.data.Model',
      fields: ['id','nombre'],
      hasMany: {model: 'Ab.model.Maquina', name: 'maquina'},
      proxy{...}
   });
  </code></pre>
  
  <p><strong>CHILD MODEL</strong></p>
  
  <pre><code>Ext.define('Ab.model.Maquina', {
      extend: 'Ext.data.Model',
      fields: ['id','nombre', 'codigo', 'estado'],
      associations: [
          {type:'belongsTo', model:'Ab.model.Marca', name: 'marca'},
      ]
      proxy:{...}
   });
  </code></pre>
  
  <p><strong>CHILD GRID</strong></p>
  
  <p>Okay, MaquinaController execute load from Store and that is not important 'cause load informations very nice. The problem is that I can't show parent data.</p>
  
  <pre><code>Ext.define('Ab.view.maquina.MaquinaList', {
      extend: 'Ext.grid.Panel',
      alias: 'widget.maquinalist',
      store: 'Maquinas',
      columns: [
          { text: _('Nombre'), flex: 1, dataIndex: 'nombre' },
          { text: _('Código Externo'), flex: 1, dataIndex: 'codigo' },
          { text: _('Estado'), flex: 1, dataIndex: 'estado' },
          { text: _('Marca'), flex: 1, dataIndex: 'marca' }    &lt;&lt;&lt; HOW CAN I SHOW MARCA?
      ]
  });
  </code></pre>
  
  <p>Thanks in advance. </p>