Added a buildName wrapper, for Build Name Setter plugin

Hi,

I've written a little "buildWrapper" wrapper method. It enables and configures the Build Name Setter plugin, which allows defining how the job builds should be named:
https://wiki.jenkins-ci.org/display/JENKINS/Build+Name+Setter+Plugin

It would be nice to merge it for next version (currently I'm using it already through WrapperContext.metaClass).

Thanks,
Thomas.