Trigger events when navbar is hidden or shown

[mariavilaro]

A hide event is fired after hiding the navbar, and a show event is fired after showing it. You can then add the custom handlers like this:

    $(document).on('show.autoHidingNavbar',function(){
        console.log('hello');
    });

Or like this:

    $('.navbar-fixed').on('hide.autoHidingNavbar',function(){
        console.log('bye');
    });

I decided to use 'autoHidingNavbar' namespace but feel free to change it to whatever you think is best!

[vladimirnani]

Good job, waiting for merge :) @istvan-ujjmeszaros