Added URL parameter to auto show and hide toolbar

Implemented hiding the toolbar when the url parameter ```toolbar=0``` is passed per issue https://github.com/mozilla/pdf.js/issues/2784

* Built on the toolbar hiding in https://github.com/mozilla/pdf.js/pull/2885
* Toolbar slides down when mouse is moved to the top of the window where the toolbar would be.
* Uses CSS transitions similar to the sidebar to hide and show the toolbar