Added hidesWhenZero to hide the badge when text is zero

Great component - works great!  I needed to hide the badge when the text was zero(0) so I added a new setting hidesWhenZero.  It is something that Apple has implemented on their own badge views.  Imagine our springboards without the hiding of zero badges :)

Thanks for your hard work!

p.s. I added a gitignore. 

-Ryan