title: Add a custom button in column header dropdown menus {EXTJS 4}
body: <p>I want a button in column header dropdown menu of grid in extjs4.
  so that i can add or delete columns which are linked in database.
  <img src="https://i.stack.imgur.com/Oefjx.png" alt="The button in red area is the one i&#39;m looking for..."></p>
  
  <p>Any help will be appreciated...
  Thankyou..:)</p>