title: export products to csv from the admin product grid
body: <p>The import products profile allows you to filter which products to export by name, sku...
  I want to have the same functionality in the manage products page.
  The admin will filter products in the grid and then click a "export" button to get the filtered products.</p>
  
  <p>How can I add the "export" button? what template/block do I need to override?
  When the admin click the button, how can I get the filtered collection?
  How can I export the filtered collection to a csv file? Can I use the dataflow for that?</p>
  
  <p>Thanks</p>