title: ExtJS defined combobox change event not firing
body: <p>I have a grid and rowEditing plugin in ExtJS 6.0.1
  One column in the grid is a custom combobox component that I've defined.
  Custom comboBox component has a change event. But it is not firing.</p>
  
  <p>Here is the codes;</p>
  
  <pre><code>**//RowEditing Plugin**
  var rowEditing = Ext.create('Ext.grid.plugin.RowEditing', {
      clicksToMoveEditor: 1,
      autoCancel: false,
      clicksToEdit: 1,
      saveBtnText: 'Kaydet',
      cancelBtnText: 'Vazgeç',
      editing: true,
      listeners: {
          edit: function (editor, context, eOpts) {
  
          }
      }
  });
  
  **//GridPanel**
  Ext.define('MailToTicketPersonsGrid', {
      extend: 'Ext.grid.Panel',
      xtype: 'MailToTicketPersonsGrid',
      id: 'mailToTicketPersonsGrid',
      store: mailToTicketPersonsStore,
      plugins: [rowEditing],
      columns: {
          items: [
              {
                  text: 'Mail',
                  flex: 1,
                  dataIndex: 'mail'
              },
              {
                  text: 'Ad',
                  flex: 1,
                  dataIndex: 'name',
                  editor: {
                      xtype: 'textfield',
                  }
              },
              {
                  text: 'Soyad',
                  flex: 1,
                  dataIndex: 'lastName',
                  editor: {
                      xtype: 'textfield',
                  }
              },
              {
                  text: 'Telefon',
                  flex: 1,
                  dataIndex: 'phone',
                  editor: {
                      xtype: 'textfield',
                  }
              },
              {
                  text: 'Şirket',
                  flex: 1,
                  editor: {
                      xtype: 'CompanySearch',                        
                  }
              }
          ]
      }
  });
  
  
  **//Window**
  Ext.create('Ext.window.Window', {
      id: 'createUserWindow',
      layout: 'fit',
      border: 0,
      resizable: false,
      modal: true,
      bodyPadding: 10,
      width: 600,
      height: 300,
      listeners: {
          show: function () {
  
          },
          close: function () {
              Ext.getBody().unmask();
          }
      },
      items: [
          {
              xtype: 'panel',
              border: 0,
              layout: {
                  type: 'vbox',
                  align: 'stretch',
                  pack: 'start'
              },
              items: [
                  {
                      xtype: 'MailToTicketPersonsGrid',//grid
                      flex: 1
                  }
              ]
          }
      ]
  }).show();
  
  
  **//Custom ComboBox**
      Ext.define('companySearch', {
      extend: 'Ext.form.field.ComboBox',
      xtype: 'CompanySearch',
      emptyText: 'Şirket ara...',
      editable: true,
      listeners: {
          change: function (field, newValue, oldValue, eOpts) {
              alert(newValue);
          }
      }
  })
  </code></pre>