(Docs) Unify OS version info, update Puppet Enterprise info

- To make things easier for the release team, we moved the OS versions supported
  by our repositories into some central files, in the source/_includes directory
  of the puppet-docs repo. Mco docs can take advantage of this too.
- We're now shipping a PE with MCollective 2.x.
Merge pull request #99 from nfagerlund/version_info

(Docs) Unify OS version info and plug Puppet Enterprise in more places