Add a failsafe parameter in gitium webhook to revert last commit

Check and experiment with this option a bit. Think about it, imagine you make a change in your theme and suddenly your site crashes, what if you could "ping" a special URL in your gitium webhook that have a password only you know and that will quickly revert your last change that broke your site?

Let's see if we can do something like this, it's just an idea for now.