Filter depending on parameters

[andrejohansson]

We have a case where we only want notifications when a build starts and have some given parameters. In our specific case we have builds that deploy our software, and we choose the target environment (dev, qa, prod) using a parameter.

In our hipchat room we are only interested in getting notified when we deploy to production since dev and qa quickly gets to chatty since they deploy continuously.

My suggestion is to add the ability to trigger notifications only if a specific paramater (or parameters) have some given values.

If this is added, #38 would be solved as well since branch name is a parameter.