Possible to use html-tags in description

Not sure if this is a security issue? 
https://wiki.jenkins-ci.org/display/JENKINS/Jelly+and+XSS+prevention

Anyway, this pull-request makes it possible to use html-tags in the description.

![build_flow_html](https://f.cloud.github.com/assets/4181469/454477/2dfb8386-b33a-11e2-85c0-6286dc30cbec.png)