Debugger bar: fixed page bottom gap caused by debug bar

Fixing this at the bottom of page.

![nette_debug_bar_line](https://f.cloud.github.com/assets/284263/377799/4cf3b98e-a4ee-11e2-8368-1bf907f2ae98.png)

It does not change appearance or behaviour. Tested Fx, Chrome, Opera, IE10.