Move newsletter to popup

This PR is for moving newsletter subscription to the popup regarding issue #9 . Popup will be shown after several seconds, when users get familiar with the site - if they like VirtKick idea, they can subscribe to the newsletter. 

To make it a little more fun, there is an alien animation included. ;-)

After moving newsletter subscription to the popup, it should be removed from the main jumbotron and new actions - demo and download - should take it's place, as shown on http://showcase.virtkick.io/virtkick-layout-homepage.png.