add package support for OpenBSD

I've been using this for a couple months on my OpenBSD boxes and it seems to work fine. I thought I'd submit it for feedback before I end up sitting on it too much longer. :)

A couple things to call out:

1. The Configurate class makes it a bit easier to deal with config files, and I especially like using it with rc.conf.local and the pkg_scripts services list, but no doubt its not for everyone. Its used for enabling and disabling services.
1. I haven't created any service tests yet.
@btm I'll change it to the Alberta, CA mirror as the fallback, preferring the use of PKG_PATH if available. I was thinking one could override the 'source' attribute if they want to use a different mirror, what do you think of that?