title: How to register for a Grid Column's Hide Event Extjs
body: <p>Does anyone know how/where to register for a grid column's hide event? I want to know when a grid's columns have been hidden or unhidden.</p>
  
  <p>I see nothing in Columns.js 
  I do see something in Ext.grid.ColumnModel but how do I register for the hiddenchange event in my controller?</p>
  
  <p>My grid is just a simple grid with columns defined in the columns array.</p>
  
  <pre><code>columns: [
         {//ID
              xtype:'templatecolumn', 
              tpl:'some template',
              header: 'ID',
              hideable:true,
              width:30,
              hidden:false,
              ...
              //other stuff
         },
         ...
         {
          //other columns
         }
  </code></pre>
  
  <p>What I want to do is in my controller register to be notified when a user has hidden a column.</p>