Add templates for FreeBSD

This is based on @mmatuska's presenstation slides and @endyman's original FreeBSD PR, but reworked to handle everything like the other templates do on FreeBSD 10.0 with pkgng.

I hope at one point the native FreeBSD installer can be used, but for now we should go with mfsBSD's zfsinstall and scripts.

Once this PR is merged, I will document everything in the wiki.