Remove nagios)* from Puppet (core)

Here we go.

I've ripped all the things I could find that should matter with regard to nagios out of core and moved them to: https://github.com/puppet-community/puppet-nagios.

There was also an old `check_puppet` and `naggen` scripts which do no seems to server any purpose anymore.

Things to figure out:

* [ ] Does everything still works?
* [ ] How do we 'deprecate' the current stuff
* [ ] How do we bring everything back together for now so that it still looks as if it's part of Puppet