Implement contact filtering

Hi,

I'm learning Backbone.Marionette, and I noticed BBClonemail's "contacts" app wasn't implemented yet.

So I gave it a shot. Feedback more than welcome !

And thanks for all the resources you put out there for beginners (blog posts, BBClonemail, etc.). They've helped me immensely, so I try to add to the resources out there (e.g. http://davidsulc.com/blog/2012/04/15/a-simple-backbone-marionette-tutorial/ )