Please re-implement it, PaginationBar object has a method show, please add other called hide and use them

https://github.com/mozilla-b2g/gaia/blob/master/apps/homescreen/js/pagbar.js#L27

And add a test for this new method

https://github.com/mozilla-b2g/gaia/blob/master/apps/homescreen/test/unit/pagbar_test.js