title: Hide column not working in ExtJs GridColumn
body: <p>In extjs I have a GridPanel. </p>
  
  <p>I want to hide some of the columns of this gridpanel, I am using  <code>Hidden="true"</code> for this and it is working fine.</p>
  
  <p>The problem is, when I click on the Grid menu, there is an option called 'Columns'. When you mouseover 'Columns' you can check/uncheck the columns you want to show/hide. </p>
  
  <p>I want to display the hidden columns in this list(unchecked) so that user can check them and manually display it on the grid.</p>
  
  <p>I tried setting  <code>Hideable="true"</code> but still these columns are not displying in the 'Columns' list.</p>
  
  <p>Please suggest a solution</p>